Harold Wilson
James Harold Wilson, Baron Wilson of Rievaulx, (11 March 1916– 24 May 1995) was a British Labour politician who served as Prime Minister of the United Kingdom from 1964 to 1970 and 1974 to 1976.
James Callaghan
Barely two years after beginning his second spell as Prime Minister, Wilson announced his surprise resignation on 16 March 1976, and unofficially endorsed Callaghan as his successor. Callaghan was the favourite to win the leadership election; although he was the oldest candidate, he was also the most experienced and least divisive. Popularity with all parts of the Labour movement saw him through the ballot of Labour MPs to win the leadership vote. On 5 April 1976, at the age of 64 years and 9 days, Callaghan became Prime Minister—the oldest person to become Prime Minister at time of appointment since Winston Churchill.