Britain is poised to witness an unprecedented era of political instability, with the resignation of Sir Keir Starmer setting the stage for a record-breaking sixth prime minister in just 10 years. Keir Starmer has announced he will resign as Labour leader, paving the way for the end of his tenure as prime minister after serving less than two years.This rapid turnover stands in stark contrast to previous periods, where the same number of leaders spanned a much longer timeframe.The past decade has seen a succession of leaders occupy Downing Street: Theresa May (2016-19), Boris Johnson (2019-22), Liz Truss (2022), Rishi Sunak (2022-24), and Sir Keir Starmer (2024-26). The next premier is due to take office by September, marking an unparalleled pace of change.By comparison, the preceding four decades saw only six individuals hold the top office: Jim Callaghan (1976-79), Margaret Thatcher (1979-90), John Major (1990-97), Tony Blair (1997-2007), Gordon Brown (2007-10), and David Cameron (2010-16). When Sir Keir Starmer’s successor takes office – which is due to happen by September – the UK will have nine living former prime ministers: another record. (Getty)Modern political history has never before recorded six different prime ministers within a single decade.While other periods have seen significant leadership changes, none match the current trajectory. Five prime ministers served between 1954 and 1964: Winston Churchill (to 1955), Anthony Eden (1955-57), Harold Macmillan (1957-63), Alec Douglas-Home (1963-64), and Harold Wilson (1964-70). A similar number held office from 1914 to 1924: Herbert Asquith (to 1916), David Lloyd George (2016-22), Andrew Bonar Law (1922-23), Stanley Baldwin (1923-24), and Ramsay MacDonald (1924).But you would need to go back to the 19th century, to a time when only a minority of the population had the vote, and the UK had yet to become a full parliamentary democracy, to find a turnover of prime ministers equivalent to that of the present day.Prime Minister Sir Keir Starmer resigned outside Number 10 (PA Wire)When Sir Keir Starmer’s successor takes office – which is due to happen by September – the UK will have nine living former prime ministers: another record.The nine prime ministers, with their current titles, are: Sir John Major, Sir Tony Blair, Gordon Brown, Lord Cameron, Baroness May, Boris Johnson, Liz Truss, Rishi Sunak and Sir Keir Starmer.They are likely to appear together in public in November, along with the new prime minister, at the Remembrance Sunday service at the Cenotaph in central London.