His decision has been prompted by his desire to step down at a relatively young age and by the unexpectedly "onerous" duties of his current role.
The 61-year-old peer, who became Lord Steel of Aikwood after the last election but prefers to be known as Sir David, said yesterday that he would still commit himself to the next four years as Presiding Officer. "I went into politics when I was very young and I have every intention of leaving it when I am reasonably young," said Sir David.
First elected to Westminster in 1965 at the age of 26, he was the youngest MP in the Commons, a fact that earned him the nickname The Boy David. His first significant political act was to introduce the controversial Abortion Bill in 1966, a move that led to an historic overhaul of Britain's abortion laws.
Elected leader of the Liberals in 1976, he managed to increase steadily the influence of the party after decades of stagnation, eventually propping up James Callaghan's Labour government with the Lib-Lab pact.
The pact was dissolved in May 1978. But when Margaret Thatcher came to power in 1979, defectors from Labour formed the Social Democratic Party (SDP). This led to a resurgence of public support with the creation of the SDP-Liberal Alliance. It was at the 1981 Liberal Assembly that Sir David ended his speech with his famous but now much-derided appeal to his party: "I have the good fortune to be the first Liberal leader for over half a century who is able to say to you at the end of our annual assembly: Go back to your constituencies and prepare for government."
The alliance between the Liberals and the SDP eventually led to the parties merging after their disastrous 1987 election results, when the Tories greatly increased their majority. Within weeks of the election, Sir David stood down to allow Paddy Ashdown to become leader of the new Liberal Democrat party.
After eight more years as an MP, he retired from the Commons in 1997 to become Lord Steel. An advocate of Scottish devolution, he was elected as a Liberal Democrat MSP for Lothians region this year.Reuse content