1820 in the United Kingdom

Incumbents

• Monarch – George III, George IV
• Regent – George, Prince Regent
• Prime Minister – Robert Jenkinson, 2nd Earl of Liverpool
• Parliament – 6th, 7th

  Events

• 29 January – George IV of the United Kingdom ascends the Throne on the death at Windsor Castle of his father George III, ending the period known as the English Regency which began in 1811. George IV has served as prince regent during this time due to his father's mental deterioration.
• 30 January – Royal Navy captain Edward Bransfield in the Williams is the first person positively to identify Antarctica as a land mass.
• 23 February – a plot to murder the Cabinet, the Cato Street Conspiracy, was exposed.
• March – general election increases Tory party majority.
• 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.
• 1 May – the Cato Street conspirators are the last to suffer decapitation following their hanging for treason outside Newgate Prison in London.
• 11 May – launch of, the ship that will take the young Charles Darwin on his scientific voyage, at Woolwich Dockyard.
• June – Pains and Penalties Bill put before Parliament to deprive Caroline of Brunswick, George IV's wife, of the title of Queen Consort. The bill is withdrawn after her public trial.
• 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 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.
• 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.
• John Keats' collection Lamia and Other Poems.
• Walter Scott's novels The Abbot and The Monastery.
• Percy Bysshe Shelley's lyrical drama Prometheus Unbound.
• The 6th Edition of Encyclopædia Britannica.
• Hone and Cruickshank's satirical work The Queen's Matrimonial Ladder.
• Publication of the last of William Blake's prophetic books, , is completed.

  Births

• 17 January – Anne Brontë, author
• 28 February – John Tenniel, illustrator
• 22 March - John Brown, English cricketer
• 30 March – Anna Sewell, writer
• 27 April – Herbert Spencer, philosopher and political theorist
• 4 May – Joseph Whitaker, publisher
• 12 May – Florence Nightingale, nurse
• 23 November – Isaac Todhunter, mathematician
• 3 December – John Coleridge, Lord Chief Justice
• 10 December – Princess Elizabeth of Clarence

  Deaths

• 23 January – Prince Edward, Duke of Kent and Strathearn
• 29 January – King George III of the United Kingdom
• 5 February – William Drennan, Irish political radical, poet and physician
• 1 May – Arthur Thistlewood, conspirator
• 30 May – William Bradley, Britain's tallest ever man
• 19 June – Sir Joseph Banks, naturalist and botanist
• 3 September – Benjamin Latrobe, architect
• 11 October – James Keir, geologist, chemist and industrialist