Events from the year 1820 in the United Kingdom. This year sees a change of monarch after a nine-year Regency.
Incumbents
Monarch – George III (until 29 January), George IV (starting 29 January) Regent – George, Prince Regent (until 29 January) Prime Minister – Robert Jenkinson, 2nd Earl of Liverpool (Tory) Foreign Secretary – Robert Stewart, Viscount Castlereagh Home Secretary – Lord Sidmouth Parliament – 6th (until 29 February), 7th (starting 21 April)
Events
8 January – General Maritime Treaty ("General Treaty for the Cessation of Plunder and Piracy by Land and Sea, Dated February 5, 1820") signed between the sheikhs of Abu Dhabi, Sharjah, Ajman, Umm Al Quwain and Ras Al Khaimah (later constituents of the Trucial States) in the Arabian Peninsula and the United Kingdom. 29 January – George IV of the United Kingdom ascends the Throne on the death at Windsor Castle of his father George III (after 59 years on the throne), ending the period known as the Regency era which began in 1811. George IV has served as prince regent during this time due to his father's mental deterioration. The title Prince of Wales falls into abeyance for 21 years. 30 January – Royal Navy captain Edward Bransfield in the Williams is the first person to positively identify Antarctica as a land mass. 23 February – a plot to murder the Cabinet, the Cato Street Conspiracy, is exposed. 10 March – Astronomical Society of London is founded. 1–2 April – a Proclamation, signed "By order of the Committee of Organisation for forming a Provisional Government", is distributed in the Glasgow area, beginning the "Radical War" in Scotland. The following day, around 60,000 – particularly weavers – stop work across a wide area of central Scotland. Disaffection spreads to the West Riding of Yorkshire. 5 April – Radical War: Troops capture radicals at Bonnybridge. 8 April – Radical War: Radical prisoners from Paisley are freed from jail in Greenock after militia have killed eight of the crowd. 14 April – 1820 United Kingdom general election, begun on 6 March, concludes with an increased Tory party majority. 1 May – the Cato Street conspirators are the last to suffer judicial decapitation in the UK following their public hanging for treason outside Newgate Prison in London (legally, a mitigation of the last sentence in Britain of hanging, drawing and quartering). 11 May – launch of , the ship that will take the young Charles Darwin on his scientific voyage, at Woolwich Dockyard. 5 June – Caroline of Brunswick, the new King's estranged wife, returns to England after six years abroad in Italy, where she has been carrying on an affair; since ascending the throne, the King has sought to receive his government's approval for a divorce. 10 June – Sir Thomas Munro is appointed as the British colonial Governor of the Madras Presidency, which encompasses most of southern India. 5 July – Pains and Penalties Bill put before Parliament to deprive Caroline of Brunswick, George IV's estranged wife, of the title of Queen Consort, leading to her de facto public trial before the House of Lords opening on 17 August. Although narrowly passed on 10 November in the House of Lords, the bill is withdrawn in the knowledge that it would almost certainly not pass the House of Commons. 26 July – opening of Union Chain Bridge across the River Tweed between England and Scotland, designed by Captain Samuel Brown. Its span of 449 ft (137 metres) is the longest in the Western world at this time, and it is the first wrought iron vehicular suspension bridge of its type in Britain. 1 August — completion and opening of the Regent's Canal through to the London Docks. 30 August – Radical War: Radical leader James Wilson, a Strathaven weaver, is executed for treason on Glasgow Green for his part in the rising. 8 September – Radical War: Radical leaders John Baird and Andrew Hardie are executed at Stirling for their part in the rising at Bonnybridge.
Publications
Friedrich Accum's exposé A Treatise on Adulterations of Food and Culinary Poisons. Hone and Cruickshank's satirical work The Queen's Matrimonial Ladder. John Keats' collection Lamia and Other Poems. Sir Walter Scott's anonymous novels The Abbot and The Monastery. Percy Bysshe Shelley's lyrical drama Prometheus Unbound. The 6th Edition of Encyclopædia Britannica. Publication of the last of William Blake's prophetic books, Jerusalem: The Emanation of the Giant Albion, is completed.