National Transmission System

The United Kingdom's National Transmission System (NTS) is the network of gas pipelines that supply gas to about forty power stations and large industrial users from natural gas terminals situated on the coast, and to gas distribution companies that supply commercial and domestic users. It covers Great Britain, i.e. England, Wales and Scotland. ^[1]

History

Origins

The system originated in the construction during 1962–3 of the 200-mile (320 km) high-pressure methane pipeline from Canvey Island (on the Essex coast) to Leeds. ^[2] Imported liquefied natural gas (LNG) from Algeria was turned into gas at the Canvey terminal and supplied to the pipeline, providing eight of the twelve area gas boards with access to natural gas. ^[3] The gas was initially used to manufacture town gas, either as a feedstock in gas reforming processes or to enrich lean gases such as that produced by the Lurgi coal gasification process.

The pipeline was 18-inch (460 mm) in diameter and operated at 1,000 pounds per square inch (69 bar). The pipeline had 150 miles (240 km) of spur lines, supplying gas to area boards. ^[4]

Methane pipeline spur lines

Area board	Supply to	Diameter (inches)	Length (miles)
North Thames	Bromley/East Greenwich 'Tee'	14	15.5
	Bromley	10	2.5
	Slough (from Reading spur line)
South Eastern	East Greenwich	12	3
Southern	Reading	8	49
Eastern	Chelmsford	12	19.9
	Hitchin	8	7
	Dunstable	6	8.5
	Watford (from Reading spur line)	12	2.1
West Midlands	Coleshill	14	10.5
East Midlands	Sheffield	12	10
North Western	Manchester	14	24
North Eastern	Leeds	12	8

The Gas Council was responsible for this £10 million co-operative scheme and the construction details were a joint effort of the distribution engineers of the area boards.

LNG had first been imported to Canvey from Louisiana in February 1959, and piped to Romford gasworks as feedstock to a reforming plant. ^[5]

UK natural gas

Natural gas was discovered on the UK continental shelf in 1965 and production started in 1967. ^[6] The development of offshore natural gas fields is shown in the following table. Shore terminals were built to receive, process, blend and distribute the gas.

UK sources of offshore natural gas, 1967–1985

Field	Field type	Licensee or operator	Discovered	First gas onshore	Shore terminal
West Sole	Gas	BP	September 1965	March 1967	Easington
Leman	Gas	Shell/Esso, Amoco/Gas Council, Arpet Group, Mobil	April 1966	August 1968	Bacton
Hewett	Gas	Phillips Petroleum, Arpet group	October 1966	July 1969	Bacton
Indefatigable	Gas	Shell/Esso, Amoco/Gas Council	June 1966	October 1971	Bacton
Viking	Gas	Conoco/BNOC	May 1968	July 1972	Viking (Theddlethorpe)
Rough	Gas	Amoco/Gas Council	May 1968	October 1975	Easington
Forties	Oil + associated gas	BP	October 1970	September 1977	St Fergus
Frigg (Norway)	Gas	TotalEnergies	June 1971	September 1977	St Fergus
Frigg (UK)	Gas	TotalEnergies	May 1972	September 1977	St Fergus
Piper	Oil + associated gas	Occidental group	January 1973	November 1978	St Fergus
Tartan	Oil + associated gas	Texaco	December 1974	January 1981	St Fergus
Brent	Oil + associated gas	Shell/Esso	July 1971	1982	St Fergus
Morecambe Bay	Gas + condensate	Hydrocarbons (GB)	September 1974	1985	Barrow

With the assured availability of natural gas, a government white paper on fuel policy ^{[7] [8]} in November 1967 proposed that natural gas should be immediately and more extensively exploited. The Gas Council and area boards began a ten-year programme to convert all users and appliances to operate on natural gas and consequently to discontinue the manufacture of town gas at local gasworks. In a pilot scheme, users on Canvey Island had been converted to natural gas in 1966. ^[9]

Building the NTS

To exploit the availability of natural gas and to provide for more widespread distribution, construction began of a major new transmission network which became the National Transmission System. ^[10]

Feeder pipelines – England

Gas from the West Sole field was first dispatched from the Easington terminal on the Yorkshire coast in July 1967, via Feeder No. 1 across the Humber to the East Midland Gas Board's gasworks at Killingholme. It was used to enrich low calorific value manufactured gas. Feeder No. 1 was extended to Totley near Sheffield where it connected to the 18-inch methane pipeline. UK natural gas first entered the NTS in July 1968. ^[11]

Feeder lines from the North Sea gas terminals to the spine of the NTS were laid and brought into use as the shore terminals were constructed. ^{[3] [12] [13] [14]}

Initial feeder pipelines of the NTS

Feeder No.	Diameter	Length	From	To	Operational
1	24-inch (600 mm)	90 miles (144 km)	Easington terminal	Scunthorpe and Totley near Sheffield, where it connected to the original methane pipeline.	July 1967/ July 1968
2	36-inch (900 mm)	123 miles (197 km)	Bacton terminal	Brisley, Eye, Peterborough and Churchover near Rugby, where it connected to the original methane pipeline.	August 1968
3	36-inch	107 miles (171 km)	Bacton terminal	Roudham Heath, Cambridge, Peters Green, Whitwell near Hitchin, where it connected to the original methane pipeline.	October 1969
4	36-inch	154 miles (246 km)	Bacton terminal	Great Ryburgh, King's Lynn, Audley and Alrewas near Lichfield.	Autumn 1970
5	36-inch		Bacton terminal	Yelverton, Diss, Stowmarket, Braintree, Chelmsford and Horndon, where it connected to the original methane pipeline	Autumn 1971
6	30-inch (750 mm)	91 miles (146 km)	Paull	Pickering (see note), Westwood and Little Burden near Darlington	Autumn 1971
7	36-inch		Wisbech	Gosberton, Hatton, Old Warden, Tydd St Giles and Scunthorpe	1972
8	30-inch		Former Viking (Theddlethorpe) terminal	Hatton	July 1972

The No. 6 feeder runs via Pickering which received gas from a treatment plant for the onshore Lockton gas field. ^[14]

Feeder pipelines – Scotland

North Sea gas first reached Scotland in Spring 1970 at Coldstream via an extension of the Leeds-Newcastle pipeline. This pipeline was then extended to Glenmavis near Coatbridge Lanarkshire (Feeder No. 12) where a natural gas liquefication plant was constructed. ^[14]

A major set of pipelines were constructed in Scotland in preparation for arrival of gas from the Frigg gas field in 1977. From the St Fergus terminal in Scotland, two 36-inch (900 mm) pipelines (Feeder No. 10 and No. 11) were laid via Bathgate to Partington and Bishop Auckland to connect to the NTS in England, a total pipeline length of 595 miles (950 km). These lines were commissioned in 1976 and cost £140 million. Initially they carried gas from southern England into Scotland until the Frigg field began production via St Fergus in September 1977. Compressor stations are provided at 40 mile (65 km) intervals along the pipelines. A third 36-inch pipeline from St Fergus (Feeder No. 12) was completed in 1978, and a fourth 40-inch (1050 mm) pipeline (Feeder No. 13) in 1982. ^[15]

Growth of the NTS

The NTS was extended from Leeds to Newcastle upon Tyne in early 1969. ^[14] This line was extended to Coldstream in spring 1970 and then to Glenmavis, near Coatbridge, Lanarkshire.

The Wales Gas Board received natural gas supplies in 1969 through a 24-inch line from Churchover (Rugby) to Swansea via Wormington (an extension to Feeder No. 2). North Wales was also connected in 1969 via a 24-inch/18-inch pipeline from Audley Cheshire to Maelor near Wrexham (an extension to Feeder No. 4). ^[14]

The South Western Gas Board received natural gas at the end of 1970 from a 24-inch/20-inch pipeline from Wormington to Exeter (Feeder No. 14). ^[14]

A 30-inch/24-inch extension of Feeder No. 3 runs to the west of London via Slough to Mogador, Surrey, and was commissioned in 1970. An extension of Feeder No. 5 runs from Horndon-on-the Hill, crosses the Thames at Tilbury and runs via Shorne to connect to Mogador, completing the South London ring main which became operational in early 1972. ^[14]

In addition to these distribution pipelines, in 1971 the area boards began to supply natural gas directly to major consumers. For example, a 24-inch 17 mile 'spine' pipeline was constructed to ICI Ltd at Billingham (designated as part of Feeder No. 6), and the West Midlands Gas Board laid six similar 'spine' mains into industrial districts of Birmingham and the Black Country. ^[14]

Most of the NTS was built from the late 1960s to the early 1980s. ^[16]

Growth of the NTS 1966–1983

Years	NTS mileage	Operational gas terminals	Compressor stations
1966/7	320	Canvey	0
1968/9	688	Canvey Easington Bacton	0
1970/1	1898	Canvey Easington Bacton	1
1972/3	2199	Canvey Easington Bacton Theddlethorpe	4
1974/5	2308	Canvey Easington Bacton Theddlethorpe	9
1976/7	2915	Canvey Easington Bacton Theddlethorpe St. Fergus	10
1978/9	3047	Canvey Easington Bacton Theddlethorpe St. Fergus	11
1983	3200	Canvey Easington Bacton Theddlethorpe St. Fergus	14

Later (post-1983) feeder mains not described above include: ^[17]

NTS Feeder pipelines built after 1983

Feeder No.	From	To	Year commissioned
9	Easington	East Ilsley	1983–86
	Brocklesby	Stallingborough
10	Bathgate	Glenmavis
	Thrunton	Saltwick
11	Bathgate	Longtown
12	Kirriemuir	Longtown via Bathgate
	St Fergus	Aberdeen
14	Barrington	Kenn South
15	Longtown	Warburton	1984
16	Barrow	Lupton	1983
	Stapleford Tawney	Stanford Le Hope (near Canvey Island)
17	Theddlethorpe	Hatton	1988
18	Peterborough	Cambridge (via Huntingdon and New Wimpole)	1988–94
	Isle of Grain	Gravesend	2008
	Matching Green	Rye House
	Matching Green	Tilbury	1990
	St Neots	Little Barford
19	Easington	Paull	1991
20	Ilchester	Choakford	1989
21	Mawdesley	Alrewas	1992–2001
	Carnforth	Burscough	1992
	Elworth	Deeside power station	1994
22	Goxhill and Hatton	Peterborough	1993
23	Churchover	Honeybourne	1998–2001
	Peterstow	Gilwern	2000
	Wormington	Corse	2000
24	St Fergus	Lochside	2001
	Easington	Paull	2010
	Hatton	Silk Willoughby	2001
25	Bridge Farm	Mickle Trafford	2001
26	Huntingdon	Steppingley	2001
27	Bacton	King's Lynn	2003
	Cambridge	Matching Green	2002
28	Herbrandston	Corse	2007
29	Easington	Nether Kellett	2006–08

The NTS now comprises over 7,600 km of welded steel gas pipelines. The Canvey to Leeds line is no longer part of the NTS.

LNG storage sites

In addition to the Canvey Island liquefied natural gas (LNG) import terminal, further LNG storage sites were constructed from the late 1960s. ^[18] These were peak-shaving facilities used to support the NTS at times of high demand, and to ensure security of gas supplies at strategic locations. When demand was high, liquefied natural gas was pumped from storage tanks, heated in vapourisers to a gaseous state and delivered into the NTS. When demand was low, gas was withdrawn from the NTS and liquefied by cryogenic cooling to minus 162 °C to replenish the storage tanks.

NTS liquefied natural gas (LNG) sites. Gas volumes at standard conditions.

Site	LNG storage tank capacity	Commissioned	Decommissioned	Operations
Canvey Island, Essex	6 × 4,000 tonnes, 2 × 1,000 tonnes, 4 × 21,000 tonnes [19] (underground)	1959, 1964, 1968, 1975	1984 [20]	Import of LNG from Arzew Algeria, original contract for 1 billion m3 (35 billion cu ft) per year of gas. Liquefication 205 tonnes/day, vapourisation 6 × 50 tonnes/hour. [21]
Ambergate, Derbyshire	5,000 tonnes (1 × 12,000 m3) [22] [21]	1967–1970 [19]	1985 [23]	Import of LNG by road tanker from Canvey, output 72 million cu ft (2.0 million m3) per day. [24]
Glenmavis, Lanarkshire	20,000 tonnes (2 × 47,800 m3), [22] [21]	1972, 1974 [21]	2012	Liquefication 100 tonnes per day, vapourisation 250 million cu ft (7.1 million m3) per day
Partington, Cheshire	4 × 20,000 tonnes (4 × 49,800 m3) [22] [21]	1972 [19] 1972, 1974 [21]	March 2012	Liquefication 10 million cu ft (280 thousand m3) per day, [25] vapourisation 8 × 75 tonnes/hour [21]
Dynevor Arms, (Hirwaun) Rhondda Cynon Taf	2 × 20,000 tonnes [22]	1972	March 2009	Liquefication 10 million cu ft (280 thousand m3) per day, [25] vapourisation 2 × 75 tonnes/hour [21]
Avonmouth, Bristol	3 × 50,000 m3	1974–1980; [19] 1978, 1979, 1983 [21]	April 2016 [26]	Short-term storage, liquefication 205 tonnes/day, vapourisation 6 × 75 tonnes/hour [21]
Isle of Grain, Kent	4 × 50,000 m3, 4 × 190,000 m3	1980–2010	Operating	Vapourisation 58 million m3/day. See Grain LNG Terminal

High-pressure gas storage

In addition to LNG storage for peak-shaving, several sites had storage facilities for high pressure gas that could be released into, and pressurised from, the NTS. The following sites were operational by 1972. ^[27]

• Isle of Grain, Kent: six 'bullets', 12 ft (3.6 m) diameter, 250 ft (76.2 m) long, capacity 8 million cubic feet (226,000 m³) of gas, operating at up to 1,000 psi (69 bar).
• Beckton gasworks, East London: eight 'bullets', 13.5 ft (4.1 m) diameter, 263 ft (80.1 m) long, capacity 5 million cubic feet (142,000 m³) of gas, pressure cycle 350-100 psi (24-6.9 bar).
• South Western Gas Board, for Bristol and Cheltenham: eleven 'bullets', 13 ft 6 in (4.1 m) diameter, 311 ft 8 in (95 m) long, total capacity 13 million cubic feet (368,000 m³), pressure cycle 450-40 psi (31-2.76 bar).
• Biggin Hill, Kent: seventeen, 42-inch (1.07 m) diameter buried pipes, 1,040 ft (317 m) long, capacity 10 million cubic feet (283,000 m³), operating up to 1,000 psi (69 bar).

Operation

The NTS is the starting point for UK gas distribution. The pipeline system serving houses is not part of the NTS, but is part of the gas distribution network of local distribution zones; the two systems combine to form the UK's gas distribution network.

The two types of gas pipelines in the UK are: large diameter high-pressure (up to 85 ^[28] bar (1200 psi) and 1050 mm (41¼") ^[28] diameter) pipelines – the type that the NTS uses – and smaller diameter lower pressure pipelines that connect to users who burn gas for heat. The wall thickness of the high-pressure pipelines is up to 0.625 inches (18mm).

Entry

Gas currently enters the NTS from a number of sources:

• Offshore oil and gas fields on the UK continental shelf. These deliver gas via five (formerly six) UK coastal gas terminals (five in England: CATS Teesside; Easington/Dimlington; Bacton; Rampside Barrow and the former Theddlethorpe terminal; and one in Scotland: St Fergus). Gas from the Liverpool Bay (Douglas) field formerly entered the NTS at Burton Point terminal in Cheshire; this terminal is now identified by National Grid as a NTS offtake to Connah's Quay power station.
• Onshore gas fields such as Saltfleetby, Lincolnshire (production was via the former Theddlethorpe terminal); and Wytch Farm, Dorset.
• Continental Europe. From Norway via the Langeled pipeline and the Easington terminal; from the Netherlands via the BBL pipeline; from Belgium via the Interconnector UK pipeline, both of the latter through Bacton gas terminal.
• Imported LNG. Gas is delivered from import terminals at the Isle of Grain and Milford Haven (South Hook and Dragon). The Canvey Island gas terminal ceased importing LNG in 1984. ^[20]
• Storage facilities. These include a mixture of salt cavity storage, onshore LNG storage sites, and formerly the depleted onshore gas field at Rough (via Easington terminal). The onshore storage facilities are listed below. The NTS was formerly supplied by the following decommissioned LNG sites: Ambergate, Derbyshire (closed 1985); Dynevor Arms, Merthyr Tydfil (closed 2009); Glenmavis, Lanarkshire (closed 2012); Partington, Greater Manchester (closed 2012); and Avonmouth, Bristol (closed April 2016). ^[26]

Gas specification and composition

The specification of gas transported within the NTS is typically within the following parameters (revised April 2023). ^{[29] [30] [31] [32]}

Specification of gas in the NTS

Content or characteristic	Value
Gross calorific value	37.0 – 44.5 MJ/m3
Wobbe number*	47.2 – 51.41 MJ/m3
Water dewpoint	<-10 °C @ 85barg
Hydrocarbon dewpoint	<-2 °C
Hydrogen sulphide content*	≤5 mg/m3
Total sulphur content (including H2S)*	≤50 mg/m3
Hydrogen content*	≤0.1% (molar)
Oxygen content*	≤0.2% (molar)
Carbon dioxide content	≤2.0% (molar)
Nitrogen content	<5.0% (molar)
Total inerts	<7.0%
Incomplete combustion factor*	≤0.48
Soot index*	≤0.60

Parameters marked * are specified in the Gas Safety (Management) Regulations 1996. ^[30]

The composition of natural gas in the NTS in 1979 was typically as shown below. ^[33] The decline of supply from the UK continental shelf since 2000 ^[34] and the sharp increase in LNG imports during the 2021 natural gas supplier crisis have made the composition more variable, though still within the calorific value limits.

Composition of natural gas, 1979

Component	Volume %
Methane	93.63
Ethane	3.25
Propane	0.69
Butane	0.27
Other hydrocarbons	0.20
Nitrogen	1.78
Carbon dioxide	0.13
Helium	0.05

Natural gas storage

Gas storage is used to manage seasonal and short-term variations in the supply and demand of gas in the UK. Facilities include salt caverns and onshore LNG storage sites (see above). Since 1985, gas has been stored offshore in the depleted Rough gas field, which initially held nine days' supply and was the UK's largest store. ^[35] This facility, owned by Centrica, was closed in 2017 due to maintenance costs ^[35] but about 20% of its capacity was reopened in October 2022. ^[36]

The operational onshore gas storage facilities in Britain are as follows. ^{[37] [38] [39]}

Onshore gas storage facilities in Britain

Facility	Location	Coordinates	Owner	Type	Gas storage volume (106 m3)	Maximum injection rate (106 m3/d)	Maximum production rate (106 m3/d)	Supply duration (days)	Connection to NTS	Commissioned
Aldborough	Aldborough, East Yorkshire	53°48'50"N 0°05'16"W	SSEHL / Equinor	Salt cavern	195	29	31	6	FM06	2009
Hatfield Moor	Hatfield, Doncaster	53°33'11"N 0°57'31"W	Scottish Power	Depleted gas reservoir	70	2	2	35	FM07	2000
Hill Top Farm	Warmingham, Cheshire East	53°08'48"N 2°26'45"W	EDF Energy	Salt cavern	20	2	2	10	FM15, FM21	2011
Hill Top Farm (with extension)	Warmingham, Cheshire East	53°08'48"N 2°26'45"W	EDF Energy	Salt cavern	56	14	14	4	FM15, FM21	2019
Hole House Farm	Warmingham, Cheshire East	53°08'49"N 2°26'44"W	EDF Energy	Salt cavern	44		8	5.5	FM15, FM21	2001 (mothballed July 2018)
Holford	Byley, Cheshire West and Chester	53°13'37"N 2°24'18"W	Uniper UK Ltd	Salt cavern	200	22	22	15	FM21	2011
Hornsea / Atwick	Hornsea, East Yorkshire	53°56'48"N 0°12'28"W	SSEHL	Salt cavern	235	3	12	20	FM06	1979
Humbly Grove	Alton,  Hampshire	51°11'39"N 1°00'37"W	Humbly Grove Energy	Depleted gas / oil reservoir	300	8	7	43	FM07, FM09 (Barton Stacey)	2005
Stublach 1	Northwich, Cheshire West and Chester	53°14'03"N 2°26'04"W	Storengy	Salt cavern	220	16	18	12	FM21	2014
Stublach 1 & 2	Northwich, Cheshire West and Chester	53°14'03"N 2°26'04"W	Storengy	Salt cavern	400	30	30	13	FM21	2019

The salt cavity storage facility at Hornsea, East Yorkshire comprises seven cavities at a depth of 6000' (1800 metres), which each store up to 60 million m³ (80 million cu. yd.) of gas at a maximum pressure of 240 bar (3500 psi). The releasable volume of gas is about half of the gross volume. During periods of low demand, gas is compressed into the cavities by electrically driven compressors and fed back onto the NTS at times of peak demand. ^[21]

Salt cavern storage facilities at Stublach were created by drilling 20" (50 cm) diameter holes through 1000' (300 metres) of rock and 820' (250 metres) of salt. This was followed by inserting metal tubes into the holes and filling the annulus with cement to create a leak-tight seal. Water was injected into the wells to dissolve the salt and create brine which was supplied to local industry for the production of bulk chemicals, such as soda ash and chlorine. The caverns created are about 300' (90 metres) in diameter and 260' (80 metres) tall (each has a volume of 339,300 m³; 443,800 cu. yd.) and are used to hold compressed gas. Stublach is the largest gas storage facility in the UK, containing up to 450 million cubic metres (590 million cubic yards) of gas. ^[39]

Compressor stations

There are 25 (mostly gas turbine driven) compressor stations and over 25 pressure regulators. Gas moves through the NTS at speeds up to 25 mph (40 km/h), depending on pressures and pipeline diameters. Compressor stations generally operate at a pressure ratio of 1:1.4 – a balance between maintaining pressure and hence flow, and the capital and running cost of the compressors. It also ensures that the temperature rise across the compressors is not high enough to require after-coolers to prevent damage to the pipeline protective coatings. On the pipelines from St Fergus, compressor stations are provided at 40 mile (65 km) intervals; each compresses the gas from about 48 bar (700 psi) at 5 °C (41°F) to 65 bar (950 psi) at 45 °C (113°F). ^[40]

Compressor stations include:

• England – Wooler, Bishop Auckland, Carnforth, Nether Kellett, Warrington, Hatton, Alrewas, Wisbech, King's Lynn, Peterborough, Churchover, Huntingdon, Cambridge, Diss, Chelmsford, Aylesbury, Lockerley and Wormington.
• Scotland – Aberdeen, Avonbridge, Kirriemuir, Moffat and St Fergus.

Initial NTS compressor stations ^[21]

Station	Gas turbines	Power rating (MW)	Commissioned
Alrewas	2 Rolls-Royce Avons	21.6	1970
Peterborough	3 Rolls-Royce Avons	35.4	1972
Churchover	3 Orendas	18.4	1972
Scunthorpe	2 Rolls-Royce Avons	23.6	1973
Chelmsford	2 Rolls-Royce Avons	23.0	1973
King's Lynn	4 Rolls-Royce Avons	47.2	1973
Cambridge	2 Rolls-Royce Avons	23.0	1974
Bishop Auckland	2 Orendas	14.4	1974
Kirriemuir	4 Rolls-Royce Avons	47.2	1977
Bathgate	4 Rolls-Royce Avons	47.2	1977
Diss	3 Rolls-Royce Avons	34.5	1977
St Fergus I	4 Rolls-Royce Avons	47.2	1977
St Fergus II	2 Rolls-Royce Maxi Avons, 3 Rolls-Royce RB211s	65.3	1978
Moffat	2 Rolls-Royce RB211s	38.6	1980
Wisbech	1 Rolls-Royce RB211, 1 Rolls-Royce Maxi Avon	32.6	1980

Offtakes

Offtakes from the NTS include those supplying industrial users, local distribution networks, storage sites and export pipelines.

• To about 71 large users such power stations and industry, either on multi-business sites such as Billingham and Runcorn or to individual companies such as INEOS Teesside.
• To inland storage sites (see 'Entry') and formerly to the offshore Rough field storage site via the Easington gas terminal.
• To the Irish interconnectors; the 24-inch 85 mile (135 km) Scotland-Northern Ireland Pipeline (SNIP) to Ballylumford, Northern Ireland, and the two 24-inch UK-Ireland Interconnectors to Dublin, both via an NTS offtake at Moffat, Scotland.
• Gas can be exported to Belgium and the Netherlands via the Interconnector UK and the BBL pipelines, both via the Bacton terminal.
• To the Gas Distribution Network of Local Distribution Zones, as follows: ^[41]

NTS Gas Distribution Network offtakes

National Grid area	Number of LDZ offtakes
Scotland	19
Northern	15
South West	13
East Midlands	13
West Midlands	12
North West	11
East Anglia	11
North East	9
Southern	8
North Thames	5
South East	5
Wales	3
Total	124

Gas distribution network

Companies that own part of this gas network, also known as the Local Transmission System (LTS), are known as gas transporters. Gas enters this network via the NTS through a pressure reduction station to the twelve gas distribution zones in Great Britain within eight distribution networks. The network covers 275,000 km (171,000 mi). The LTS is managed from Hinckley, Leicestershire (former headquarters of the NTS). Financial transactions between gas transporters are managed by Xoserve, based in Solihull, which was a department of National Grid before it became an independent company.

For retail distribution, Cadent owns the network in North West England, the West Midlands, the East Midlands, the East of England and North London. In the North of England, local distribution is owned by Northern Gas Networks; in the Wales and West by Wales and West Utilities; and in Southern England and Scotland by SGN.

Ownership

The transmission network is owned by National Gas, which is owned by Macquarie Asset Management (80%) and National Grid plc (20%). ^[42] Agreement was reached in July 2024 for Macquarie to buy National Grid's stake, giving Macquarie full ownership in the first quarter of 2025 subject to regulatory approval. ^[43]

The changing ownership of the NTS reflects developments and corporate changes in the UK's gas and energy industries.

• Gas Council and area boards, 1962 – 31 December 1972
• British Gas Corporation, 1 January 1973 – 24 August 1986
• British Gas plc, 24 August 1986 – 1994
• Transco plc, part of British Gas plc, 1994 – 17 February 1997
• Transco plc, part of BG plc, 17 February 1997 – 1999
• Transco plc, part of BG Group plc, 1999 – 23 October 2000
• Transco plc, part of Lattice Group plc, 23 October 2000 – 21 October 2002
• Transco plc, part of National Grid Transco plc, 21 October 2002 – 31 January 2023; renamed National Grid Gas plc on 10 October 2005
• National Grid Gas plc, owned by Macquarie, BCI and National Grid, from 31 January 2023; renamed National Gas Transmission plc on 6 February 2023

Northern Ireland

Northern Ireland is not part of the NTS and gets its gas via the Scotland-Northern Ireland pipeline (SNIP), owned by Premier Transmission and built between 1994 and 1996. The gas network in Northern Ireland is split, with one area owned by Phoenix Natural Gas and the other by Firmus Energy.

See also

• Humber Gas Tunnel
• Central Area Transmission System
• United Kingdom–Ireland natural gas interconnectors

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External links

• Gas Transmission System Operations
• Map of the NTS at National Grid
• Detailed map of the NTS
• Instantaneous gas flows into the NTS
• Pipeline projects at National Grid plc
• Ownership of the gas distribution network, archived in 2008
• Society of British Gas Industries, archived in 2012
• Xoserve
• GCSE PDF factsheet about the NTS, archived from www.energynetworks.org in 2011
• Origins and Growth of the British Gas Plant Operations Department (including pipeline maps) www.oldflames.org.uk
• Statement of Gas Transmission Transportation Charges Table 3 & 5