The newspaper says Mr Birt was a paid-up member until March 1992, eight months after he was designated director-general, but gave it up almost a year before he took over the post.

The BBC confirmed Mr Birt had been a member of the Labour Party.

A BBC statement said: "John Birt gave up his membership at least a year before becoming director-general and there is no suggestion that prior to that he played any active role in the party."

Successor row

Dyke: Candidacy questioned

The report coincides with controversy over the appointment of Sir John's successor.

One of the front runners for the post, millionaire chairman of Pearson Television Greg Dyke, was described as "unacceptable" by the leader of the Conservative Party, William Hague, because he had made cash donations to the Labour Party thought to be worth about £50,000.

In a letter to BBC Chairman Sir Christopher Bland on Wednesday, Mr Hague said: "It would be totally unacceptable for anyone who has substantially and recently financially supported a political party ... to be appointed director-general of the BBC."

Although it did not name Mr Dyke, a Conservative Party spokesperson confirmed the letter referred to him.