Declarations of war by Great Britain and the United Kingdom

A declaration of war is a formal declaration issued by a national government indicating that a state of war exists between that nation and another.

In the United Kingdom, the government and command of the armed forces is vested in the sovereign. Under the sovereign, direct control of the armed forces is divided between the government and the Defence Council.^[1] However, a constitutional convention has developed regarding parliamentary approval for military action.

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:

Mr Harvey [Halifax's Private Secretary to whom Fitzmaurice's reply was sent].
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 from the Act of Union in 1707 until the creation of the United Kingdom of Great Britain and Ireland in 1801.

War or conflict	Opponent(s)	Initial authorisation	Declaration	Monarch	Prime Minister	Conclusion
War of the Quadruple Alliance	Spain	17 December 1718		George I	None	Treaty of The Hague, 17 February 1720.
War of Jenkins' Ear	Spain	23 October 1739		George II	Robert Walpole	Treaty of Aix-la-Chapelle, 18 October 1748.
War of the Austrian Succession	France	31 March 1744			Henry Pelham	Treaty of Aix-la-Chapelle, 18 October 1748.
Seven Years' War	France	17 May 1756	Declaration on France		Thomas Pelham-Holles	Treaty of Paris, 10 February 1763. British victory.
Seven Years' War	Spain	4 January 1762	Declaration on Spain	George III	Thomas Pelham-Holles	Treaty of Paris, 10 February 1763. British victory.
American Revolutionary War	France	17 March 1778	Declaration on France		Lord North	Treaty of Versailles, 3 September 1783.
American Revolutionary War	Spain	1779	Declaration on Spain			Treaty of Versailles, 3 September 1783.
Fourth Anglo-Dutch War	Dutch Republic	December 1780	Declaration on the Dutch Republic			Treaty of Paris, 20 May 1784.

Declarations of war by the United Kingdom

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".

War or conflict	Opponent(s)	Initial authorisation	Declaration	Monarch	Prime Minister	Conclusion
Napoleonic Wars	France	18 May 1803		George III	Henry Addington	Treaty of Paris (1815) and Congress of Vienna
Crimean War	Russia	28 March 1854	Declaration on the Russian Empire	Victoria	Earl of Aberdeen	Treaty of Paris, 30 March 1856
Bhutan War	Bhutan	November 1864	Declaration on Bhutan		Viscount Palmerston	Treaty of Sinchula, 11 November 1865
Anglo-Zulu War	Zulu Kingdom	18 March 1879	Ultimatum by Sir Henry Bartle Frere		Benjamin Disraeli	The war ended the Zulu nation's independence.
Anglo-Zanzibar War	Zanzibar	27 August 1896	Ultimatum by Rear-Admiral Harry Rawson		Marquess of Salisbury	The war replaced Khalid bin Barghash as Sultan with Hamoud bin Mohammed, leading to the abolition of slavery.
First World War	Germany	4 August 1914	Declaration on Germany	George V	H. H. Asquith	Armistice with Germany, 11 November 1918. Treaty of Versailles, 28 June 1919.
	Austria-Hungary	12 August 1914	Declaration on Austria-Hungary			Austria: Treaty of Saint-Germain-en-Laye, 10 September 1919. Hungary: Treaty of Trianon, 4 June 1920.
	Ottoman Empire	5 November 1914	Declaration on the Ottoman Empire			Treaty of Lausanne, 24 July 1923.
	Bulgaria	15 October 1915	Declaration on Bulgaria			Treaty of Neuilly-sur-Seine, 27 November 1919.
Second World War	Germany	3 September 1939	United Kingdom declaration of war on Germany (1939)	George VI	Neville Chamberlain	Treaty on the Final Settlement with Respect to Germany, 12 September 1990. The Potsdam Agreement on 2 August 1945 agreed the subdivision of Germany following the surrender on 8 May 1945. Austria was part of Germany when War was declared, and was formally re-established by the Treaty of Vienna on 15 May 1955.
	Italy	11 June 1940	Declaration on Italy		Winston Churchill	Armistice with Italy, 3 September 1943. The final peace treaty between Italy and the Allies was signed in Paris on 10 February 1947.
	Finland	5 December 1941^[7]	Declaration on Finland			Moscow Armistice, 19 September 1944. The final peace treaty between Finland and the Allies was signed in Paris on 10 February 1947.
	Hungary	5 December 1941^[7]	Declaration on Hungary			The final peace treaty between Hungary and the Allies was signed in Paris on 10 February 1947.
	Romania	5 December 1941^[7]	Declaration on Romania			Armistice with Romania, 12 September 1944. The final peace treaty between Romania and the Allies was signed in Paris on 10 February 1947.
	Japan	8 December 1941	Declaration on Japan			Treaty of San Francisco, 8 September 1951. This followed the Surrender of Japan on 15 August 1945 and the Occupation of Japan which began on 28 August 1945.
	Bulgaria	13 December 1941	Declaration on Bulgaria			Armistice with Bulgaria, 28 October 1944. The final peace treaty between Bulgaria and the Allies was signed in Paris on 10 February 1947.
	Thailand	25 January 1942	Declaration on Thailand			Anglo-Thai Peace Treaty, 1 January 1946