A spokesman for Mr Mandelson said Sir Christopher had written to apologise for remarks made by gay columnist and former Tory MP Matthew Parris.

The Conservative Party says it is writing to the BBC Director-General, Sir John Birt, to protest about an instruction not to allow any mention of the private life of Trade and Industry Secretary Peter Mandelson.

The party said two Shadow Cabinet members had been asked to obey the ruling.

The Tories are protesting about an instruction issued to BBC staff on Friday.

It was first challenged publicly that evening on Any Questions.

David Willetts: Mr Mandelson is being made a special case

The party's Education Spokesman David Willetts said that while he supported the BBC's policy of not seeking to intrude into the private lives of politicians, he thought Mr Mandelson was being made a special case. That was wrong, he added.

The Conservatives say their chairman Michael Ancram - a guest on Sunday morning's Breakfast with Frost on BBC TV - was also ordered not to mention Mr Mandelson's private life.

The party's Media and Culture Spokesman, Peter Ainsworth, intends to write to Sir John, protesting at what he says is an attempt to suppress discussion.

The BBC has issued a statement saying it does not report speculation about the private lives of public figures unless there is some wider issue of public concern.

The corporation said it had merely reminded programmes that those rules applied as much to Peter Mandelson as anyone else.