There has been a long-running debate[2][3] regarding whether Parliament alone should have the power to declare war and more widely to commit British forces to armed conflict. This was attempted (to the limited extent of possible war against Iraq) in 1999 with the introduction of the Military Action Against Iraq (Parliamentary Approval) Bill. However Queen Elizabeth II, acting upon the advice of her government at the time, refused to grant her consent[4] to allow the bill to be debated in Parliament and so it was dropped (Queen's Consent was needed before debate could take place because the bill affected the royal prerogative).[4] The Constitutional Reform and Governance Act 2010 originally included a section that would have required Parliamentary approval for use of the armed forces, but this was dropped from the bill before royal assent.[citation needed]
There have been no declarations of war since the Second World War (against Thailand in 1942, to be precise),[5] though British Armed Forces have taken part in armed conflict on numerous occasions nonetheless. It is considered, in light of developments in international law since 1945, notably the Charter of the United Nations, that a declaration of war is now redundant as a formal international legal instrument.[5]
The procedure for a declaration of war is set out in a letter dated 23 August 1939 from Gerald Fitzmaurice. It reads:
The Secretary of State's enquiry about how we declare war. The method of procedure is to deliver a declaration of war to the diplomatic representative in London of the enemy Power or Powers at such hour as may be decided upon by the Cabinet and to obtain a receipt recording the time of delivery. The declaration is delivered by a special messenger who should take with him the special passports covering the enemy representative, his family and personal staff and his diplomatic staff and their families. These are now being drafted on the assumption that war would in the first place be only declared on Germany and the Secretary of State would have to sign them.
It is not possible to state definitely at present what the terms of the declaration of war itself would be as these must depend upon circumstances. It is quite likely that our declaration of war might be preceded by an ultimatum which would be delivered in Berlin. This might e.g. take the form that if by a certain time the German Government had not given an assurance that they would proceed no further with their violation of Polish territory the Ambassador had instructed to ask for his passports and that His Majesty's Government would have to take such steps as might seem good to them. In such a case our actual declaration of war on the expiry of the time limit would take the form of notifying the German Embassy that no satisfactory reply having received from the German Government, His Majesty's Government considered that a state of war between the two countries existed as from a certain time.
I understand that the declaration would be drafted in consultation with the Dominions Office.
Once the declaration has been delivered a lot of consequential results follow, such as informing the other Government Departments that war has been declared and giving the same information to the diplomatic representatives in London of non-enemy powers and so forth. Standing drafts for all these purposes exist.[6]
Declarations of war by the Kingdom of Great Britain
The following table refers to declarations of war since the creation of the United Kingdom in 1801. In 1927 the United Kingdom of Great Britain and Ireland was renamed the "United Kingdom of Great Britain and Northern Ireland".
The British Armed Forces are the military forces responsible for the defence of the United Kingdom, its Overseas Territories and the Crown Dependencies. They also promote the UK's wider interests, support international peacekeeping efforts and provide humanitarian aid.
The Bill of Rights 1689 is an Act of the Parliament of England that set out certain basic civil rights and changed the succession to the English Crown. It remains a crucial statute in English constitutional law.
The monarchy of the United Kingdom, commonly referred to as the British monarchy, is the form of government used by the United Kingdom by which a hereditary monarch reigns as the head of state, with their powers regulated by the British Constitution. The term may also refer to the role of the royal family within the UK's broader political structure. The monarch since 8 September 2022 is King Charles III, who ascended the throne on the death of Queen Elizabeth II, his mother.
The Potsdam Declaration, or the Proclamation Defining Terms for Japanese Surrender, was a statement that called for the surrender of all Japanese armed forces during World War II. On July 26, 1945, United States President Harry S. Truman, United Kingdom Prime Minister Winston Churchill, and Chairman of China Chiang Kai-shek issued the document, which outlined the terms of surrender for the Empire of Japan, as agreed upon at the Potsdam Conference. The ultimatum stated that, if Japan did not surrender, it would face "prompt and utter destruction."
In a parliamentary or semi-presidential system of government, a reserve power, also known as discretionary power, is a power that may be exercised by the head of state without the approval of another branch or part of the government. Unlike in a presidential system of government, the head of state is generally constrained by the cabinet or the legislature in a parliamentary system, and most reserve powers are usable only in certain exceptional circumstances.
The Emergency Powers (Defence) Act 1939 was emergency legislation passed just prior to the outbreak of World War II by the Parliament of the United Kingdom to enable the British government to take up emergency powers to prosecute the war effectively. It contained clauses giving the government wide powers to create Defence Regulations by Order in Council. These regulations governed almost every aspect of everyday life in the country during the War. Two offences under the regulations were punishable with death. Following the conclusion of the war, the 1939 Act was repealed, with the individual regulations gradually following suit. As of 2023, at least one Regulation remains in force.
British parliamentary approval for the invasion of Iraq was given by the elected members of the House of Commons to Tony Blair's government on the eve of the 2003 invasion of Iraq, in a series of two votes, on 18 March 2003.
The government of the United Kingdom declared war on the Empire of Japan on 8 December 1941, following the Japanese attacks on British Malaya, Singapore, and Hong Kong on the previous day as well as in response to the bombing of the US fleet at Pearl Harbor.
The royal prerogative is a body of customary authority, privilege, and immunity attached to the British monarch, recognised in the United Kingdom. The monarch is regarded internally as the absolute authority, or "sole prerogative", and the source of many of the executive powers of the British government.
The government of the United Kingdom, officially His Majesty's Government, abbreviated to HM Government, is the central executive authority of the United Kingdom of Great Britain and Northern Ireland. The government is led by the prime minister who selects all the other ministers. The country has had a Labour government since 2024. The prime minister Keir Starmer and his most senior ministers belong to the supreme decision-making committee, known as the Cabinet.
The Fixed-term Parliaments Act 2011 (FTPA) was an Act of the Parliament of the United Kingdom which, for the first time, set in legislation a default fixed election date for general elections in the United Kingdom. It remained in force until 2022, when it was repealed. Since then, as before its passage, elections are required by law to be held at least once every five years, but can be called earlier if the prime minister advises the monarch to exercise the royal prerogative to do so. Prime ministers have often employed this mechanism to call an election before the end of their five-year term, sometimes fairly early in it. Critics have said this gives an unfair advantage to the incumbent prime minister, allowing them to call a general election at a time that suits them electorally. While it was in force, the FTPA removed this longstanding power of the prime minister.
Head of the Armed Forces is the position of the sovereign of the United Kingdom as commander-in-chief of the British Armed Forces. Supreme military authority vests in the monarch and extends to the exercise of several personal prerogatives. However, routine administration of the military is delegated as a matter of law to the Defence Council of the United Kingdom, a body officially charged with the direction and command of the Armed Forces. As the Defence Council and its service boards are all a part of the Ministry of Defence, which itself is a ministerial department of the Government of the United Kingdom, the prime minister makes the key decisions on the use of the Armed Forces, while the secretary of state for defence assists the prime minister in the development of defence policy and administers the day-to-day military operations.
The royal prerogative is a body of customary authority, privilege, and immunity recognized in common law as belonging to the sovereign, and which have become widely vested in the government. It is the means by which some of the executive powers of government, possessed by and vested in a monarch with regard to the process of governance of the state, are carried out.
The Constitutional Reform and Governance Act 2010, or CRAG Act, is an Act of the Parliament of the United Kingdom on UK constitutional law which affected the civil service and the ratification of treaties, and made other significant changes. It extends to all parts of the United Kingdom.
A declaration of war by Canada is a formal declaration issued by the Government of Canada indicating that a state of war exists between Canada and another nation. It is an exercise of the royal prerogative on the constitutional advice of the ministers of the Crown in Cabinet and does not require the direct approval of the Parliament of Canada, though such can be sought by the government. Since gaining the authority to declare war as a consequence of the Statute of Westminster, 1931, Canada has done so only during the Second World War.
Armed Forces Bill was a bill of the Parliament of the United Kingdom. It attempted to limit the royal prerogative of declaring war by providing that only Parliament declare war or, except in certain emergencies, could sanction the United Kingdom's participation in armed conflicts.
A declaration of war by Canada against Germany was made by order-in-council signed by George VI, King of Canada, on 10 September 1939, seven days after the United Kingdom and France had also entered a state of war with the Nazi regime. The royal proclamation of the Canadian declaration was published in the Canada Gazette.
In 2011, the government of the United Kingdom acknowledged that a constitutional convention had developed whereby the House of Commons should have an opportunity to debate the matter before troops are committed. It said that it proposed to observe that convention except when there was an emergency and such action would not be appropriate.
The powers of the prime minister of the United Kingdom come from several sources of the UK constitution, including both statute and constitutional convention, but not one single authoritative document. They have been described as "...problematic to outline definitively."
Section 9 of the Constitution Act, 1867 is a provision of the Constitution of Canada which vests the executive power in the monarch.
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