Technically, this is done by the Queen in a short ceremony at Buckingham Palace.
She always chooses the leader of the political party with the majority in the House of Commons.
Changes of PM only happen after General Elections or when the party in power changes its leader.
Spencer Perceval is the only British Prime Minister to be assassinated, he was shot in 1820.
Henry John Temple, The Viscount Palmerston, was the British Prime Minister during that time period.He was in office for the second time from June, 12 1859 - October, 18 1865
The United Kingdom's Prime Minister Neville Chamberlain.
Winston Churchill
The oldest British Prime Minister to assume office was William Ewart Gladstone, who was 84 years old when he became Prime Minister for the fourth time in 1892. He had a long political career, serving in various capacities, including as Prime Minister on four separate occasions. Gladstone is noted for his significant contributions to British politics and liberal reforms during the 19th century.
Spencer Perceval is the only British Prime Minister to be assassinated, he was shot in 1820.
No British Prime Minister has been in office for anything LIKE this long- the longest serving Prime Minister to date has been Lord Liverpool, who was in office from 1812 to '27, a total of 15 years.
Darcy Boyce is the Minister in the Office of the Prime Minister for Barbados.
Bouasy Lovansay is the Minister to the Prime Minister's Office for Laos.
Pitso Maisa is the Minister in the Prime Minister's Office for Lesotho.
Vidar Helgesen is the Minister at the Office of the Prime Minister for Norway.
Warathep Ratthanakon is the Minister to the Prime Minister's Office for Thailand.
Margaret Thatcher (Conservative) was Prime Minister of the United Kingdom from 1979 to 1990, making her the holder of that office in 1982.
The last British prime minister to die in office was Sir Winston Churchill, who served from 1940 to 1945 and again from 1951 to 1955. However, he did not die while actively in office; the last prime minister who did was Lord Palmerston, who passed away in 1865 while serving as prime minister. Churchill resigned in 1955 and died in 1965, after his political career had ended.
Abdul Wahid Omar is the Minister in the Prime Minister's Office for Malaysia.
Herbert Asquith- he had been in office since 1908, but was replaced by his Chancellor David Lloyd George in 1916 in the middle of WW1.
Hailemariam Desalegn is the Prime Minister of Ethiopia in 2013.Haliemariam became acting prime minister on 2012 August 20, officially becoming prime minister on Sept 21. He replaced long time Prime Minister Meles Zenawi Asres whom died in office.