1720 in Great Britain

• Monarch – George I

• 10 February – Edmond Halley is appointed Astronomer Royal by George I
• 17 February – Treaty of The Hague signed between Britain, France, Austria, the Dutch Republic and Spain ending the War of the Quadruple Alliance.{{cite book|last=Williams|first=Hywel|title=Cassell's Chronology of World History|url=https://archive.org/details/cassellschronolo0000will/page/297|url-access=registration|location=London|publisher=Weidenfeld & Nicolson|year=2005|isbn=0-304-35730-8|pages=[https://archive.org/details/cassellschronolo0000will/page/297 297–298]}}
• April – "South Sea Bubble": A scheme for the South Sea Company to take over most of Britain's unconsolidated government debt massively inflates share prices.
• 15 April – Ralph Allen of Bath is appointed to farm Cross and Bye Posts (i.e. to manage mail not going via London), leading to his reform of the system.{{cite book|first=Richard|last=Blake|title=The Book of Postal Dates, 1635–1985|location=Caterham|publisher=Marden|page=3}}{{cite web|url=http://www.bathpostalmuseum.co.uk/explore/biographies/ralphallen.html |title=Ralph Allen Biography |publisher=Bath Postal Museum |accessdate=2009-08-21 |url-status=dead |archiveurl=https://web.archive.org/web/20090607024648/http://www.bathpostalmuseum.co.uk/explore/biographies/ralphallen.html |archivedate=2009-06-07 }}
• 23 April (St George's Day) – George I publicly reconciles with his son George, Prince of Wales at St James's Palace
• 1 June – British silversmiths are once again allowed to use sterling silver after 24 years of being limited to a purer (but softer) Britannia silver.
• 11 June
• Robert Walpole and his ally and brother-in-law Charles Townshend rejoin the government as Paymaster of the Forces and Lord President of the Council ending the Whig Split lasting since 1717. Within a year they will be Prime Minister and Northern Secretary respectively.
• Parliament approves the Bubble Act (formally the Royal Exchange and London Assurance Corporation Act 1719), prohibiting the formation of joint-stock companies except by royal charter.
• 25 June – "South Sea Bubble" reaches its peak as South Sea Company stock is priced at £1,060 a share.
• 12 July – Under authority of the Bubble Act, the Lords Justices attempt to curb some of the excesses of the stock markets during the "South Sea Bubble". They dissolve a number of petitions for patents and charters, and abolish more than 80 joint-stock companies of dubious merit, but this has little effect on the creation of "Bubbles", ephemeral joint-stock companies created during the hysteria of the times.{{cite book|first=Charles|last=MacKay|author-link=Charles Mackay (author)|title=Extraordinary Popular Delusions and the Madness of Crowds|publisher=Harriman House Classics|year=2003}}
• September – "South Sea Bubble": share prices, led by those of the South Sea Company, collapse."Commerce", in A Cyclopedia of Commerce and Commercial Navigation, vol. 1, ed. by J. Smith Homans (Harper & Brothers, 1859) p391.
• 16 November – Pirate captain John Rackham (captured on 22 October) is brought to trial at Spanish Town in Jamaica; he is hanged at Port Royal two days later. Most of his crew is also hanged but female pirates Mary Read and Anne Bonny are spared.
• 29 December – Haymarket Theatre opens in London.

• Richard Mead's treatise A Short Discourse concerning Pestilential Contagion, and the Method to be used to prevent it.

• 13 January – Richard Hurd, bishop and writer (died 1808)
• 27 January (bapt.) – Samuel Foote, dramatist and actor (died 1777)
• 9 March – Philip Yorke, 2nd Earl of Hardwicke, politician (died 1790)
• 8 May - William Cavendish, 4th Duke of Devonshire, Prime Minister (died 1764){{cite web |title=History of William Cavendish Duke of Devonshire - GOV.UK |url=https://www.gov.uk/government/history/past-prime-ministers/william-cavendish-duke-of-devonshire |website=www.gov.uk |access-date=19 June 2023 |language=en}}
• 18 July – Gilbert White, naturalist and cleric (died 1793)
• 18 August – Laurence Shirley, 4th Earl Ferrers, murderer (died 1760)
• 30 August – Samuel Whitbread, brewer and politician (died 1796)
• 31 December – Charles Edward Stuart, pretender to the British throne (died 1788)

• 31 January – Thomas Grey, 2nd Earl of Stamford, privy councillor (born c. 1645)
• 20 April – George Gordon, 1st Earl of Aberdeen, Lord Chancellor of Scotland (born 1637)
• 5 August – Anne Finch, Countess of Winchilsea, English poet (born 1661)
• 9 August – Simon Ockley, orientalist (born 1678)
• 18 August – Matthew Aylmer, 1st Baron Aylmer, admiral (born c. 1650)
• 18 November – John Rackham, pirate

• 1720 in Wales

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