When Gordon Brown succeeds to the office later this year, as is expected, he will become the latest in a long line of prime ministers (14 in the 20th century) who entered Number 10 following the resignation or retirement of their predecessor. Of the four prime ministers in the past 30 years, two (Margaret Thatcher and Tony Blair) won general elections to become prime minister, while two (James Callaghan and John Major) succeeded mid-term.
Mr Major was catapulted into the top job at short notice and it is not surprising that his wife admitted that "the transition was a nightmare for both of us". Even where there has been an heir apparent, a smooth transition is un-usual - there was a lot of bad blood and personal tension the last time it happened, with Winston Churchill and Anthony Eden, in the 1950s.
