The SDP was official launched by the 'gang of four' in March 1981
Twenty-five years on from its launch, what impact did the Social Democratic Party have on British political life?
In a two part Sunday Supplement series broadcast in February and March 2006, Mark D'Arcy looks back at the party that was supposed to put an end to two-party politics.
He discovers that, rather than smashing Labour or the Conservatives, the legacy of the SDP was to provide a host of politicians and advisors for them.
In part one, he discovers how a number of younger SDP activists went on, after the party was wound-up, to be leading advisors to John Major's Conservative government and William Hague's opposition.
Mark D'Arcy is a BBC Parliamentary Correspondent
In part two of his series exploring how many of the SDP lost a party but still won power, Mark D'Arcy talks to the social democrats who made their peace with New Labour and found a place at the heart of Government.