oD: What's to stop a serving Prime Minister from going on and on in office?
PR: A British Prime Minister serves only as long as he or she has a majority in the House of Commons. Normally, this is ended when the governing party loses a general election and the leader of the winning party becomes PM-- as in 1945, 1951, 1964, 1970, 1974, 1979 and 1997.
Very rarely, only twice in the 20th century, did a PM lose a vote of confidence in the Commons. This happened most recently in March 1979. The ruling Labour Party was in a minority and other parties would not back it in a vote of confidence. The then PM, James Callaghan, immediately announced a general election. This took place five weeks later. Margaret Thatcher's Tories won and she became PM.
Otherwise, between general elections, PMs normally change when they resign voluntarily or lose the confidence of their own parties in Parliament. Winston Churchill left in 1955 largely because of old age and the increasing hostility of his own Cabinet. Anthony Eden left in 1957 because of a combination of ill health and loss of political confidence after the Suez fiasco. Harold Macmillan went in 1963 because of ill health. Harold Wilson left in 1976 because of age and what turned out to be ill health ( this was a surprise). Thatcher was forced out in 1990 (see below). Tony Blair went in 2007 for several reasons. He had promised not to seek a fourth term. There was also hostility within the Labour Party as well as from his successor Gordon Brown, who had been trying to force him out. An attempted coup by allies of Brown in September 2006 forced Blair to say he would step down within 12 months, as he did.
In general, British transitions from one PM to the next are smooth even when the party in office changes.
oD: What are the mechanisms for removing a serving PM?
PR: Apart from loss of a general election and loss of a vote of confidence, the main mechanism is an internal party revolt. This can occur both informally through the actions of Cabinet colleagues ( as with Churchill, Eden, and, to some extent, Blair) and formally ( notably Thatcher).
Each of the main parties has different rules about how a leader can be challenged when their party is in office. There are normally high hurdles to prevent frivolous challenges. In autumn 1990, the challenge came from Michael Heseltine, a former member of the Thatcher Cabinet who had resigned in disagreement with her in 1986. Under the Tories' then rules, a candidate not only needed to win a majority of the votes cast but also an additional margin. Thatcher won more votes than Heseltine but did not win by a sufficient margin. This forced a second ballot and Thatcher was then persuaded by her own Cabinet to step down rather than risk the humiliation of being defeated on the second round. This opened the way for John Major, then Chancellor of the Exchequer or finance minister, to enter the contest. He beat Heseltine and Douglas Hurd, the Foreign Secretary. So Thatcher was forced out by a combination of her own Conservative backbenchers and her own Cabinet colleagues. As she often pointed out, she was not defeated in the House of the Commons and she was never defeated in a general election.
oD: Can parliament vote a Prime Minister out?
PR: Yes, as stated above. But only the House of Commons (the elected house), not the House of Lords (largely unelected), on a specific vote of confidence. This would normally trigger a general election.
oD: Could Blair have appointed himself to another key job in government on resigning as PM?
PR: No. When a PM resigns he reverts to being a backbencher (that is to say an ordinary) member of the Commons ( though Blair stepped down as an Member of Parliament on the same day as he resigned as PM.) The allocation of posts in a new government is entirely dependent on the new PM. In most cases, resigning PMs, even reluctant ones like Thatcher, do not want to serve in their successor's government and often leave parliament at the general election after they have stepped down. There are a few cases of former PMs returning, after an interval, to serve in a Cabinet, as both Lord Balfour and Lord Home did as Foreign Secretaries. The rare exceptions are in coalition governments, or in wartime emergences. For instance, Neville Chamberlain remained in the War Cabinet for a few months (until he died) after handing over to Churchill as PM in May 1940.
oD: What happened to Churchill?
PR: Churchill had been on the sidelines throughout the 1930s, out of sympathy with his own party. But he was brought back into the Cabinet when the war started in September 1939. And in the spring of 1940, after wartime setbacks, when Neville Chamberlain came under fire, not least from his own Conservative MPs in a big Commons revolt, Churchill was the obvious successor. Initially, he became PM, not leader of the Conservative Party, though he did take this on after Chamberlain died later in the year.
As noted above, he left office first in 1945 after Labour won the general election ( to the surprise of Stalin who assumed that the election would be fixed). Then, after returning to power in 1951, he finally resigned in April 1955 when he had clearly become too old and ill and was being pushed out by his own Cabinet.
