The title Father of the House is given to the MP with the longest unbroken service in the House of Commons.
The Conservative MP Sir Peter Tapsell became Father of the House after the 2010 election, succeeding Labour backbencher Alan Williams, who became Father of the House after the 2005 election.
Before that, Sir Edward Heath held the position from 1992, then Tam Dalyell from 2001.
Last century a number of other ex-prime ministers were Fathers of the House.
One, David Lloyd George, was Father for the longest time - 15 years. Another, Sir Henry Campbell-Bannerman, was PM and Father simultaneously in 1907-8.
When two MPs have served for an identical period, the one who took the Oath first becomes Father.
Thus, Sir Bernard Braine - now Lord Braine - assumed the title in 1987 rather than (Sir) Edward Heath although both had been elected in 1950.
Michael Foot had first become an MP in 1945, but his service had not been continuous.