Mr Portillo, selected as Tory candidate for the Kensington and Chelsea by-election, also hinted that he might support reducing the age of consent for homosexual sex from 18 to 16.

Gay rights campaigners have accused Mr Portillo of hypocrisy for previously opposing a reduction in the age of consent to 16 and his support for the ban on gays in the military, after his admission of gay experiences in his youth.

That admission prompted former Tory chairman Lord Tebbit to say that Mr Portillo was less than frank about the duration of his homosexual phase.

Lord Tebbit: Portillo "not completely honest"

Lord Tebbit said: "He owned up to a homosexual phase when he was not much more than a schoolboy...The truth of the matter is something different. What worries me about that is that he was not completely honest."

But in an interview with The Sunday Telegraph, Mr Portillo said he had written to Lord Tebbit to protest about his comments.

Mr Portillo said: "Well, Lord Tebbit is just completely inaccurate in that respect and I have written to Lord Tebbit telling him he was completely inaccurate and I have not had a reply."

On the equalisation of the age of consent, Mr Portillo said: "I think there are two competing considerations. One is a case for equality; the other is consideration of protection for minors. I think these are quite finely balanced.

"Actually, I'm not quite sure how I would vote on the age of consent now. As I say, I think the arguments are quite finely balanced."

Mr Portillo lost his Enfield Southgate seat to Labour MP Stephen Twigg in one of the most memorable results of the 1997 General Election.

Mr Portillo was last week chosen as the Tory candidate to contest the November 25 by-election in true-blue Kensington and Chelsea, brought about by the death of Tory maverick Alan Clark.

The candidates who have announced they will contest the by-election so far are:

• Conservative Party: Michael Portillo
• Labour Party: Robert Atkinson
• Liberal Democrats: Robert Woodthorpe Browne
• UK Independence Party: Damian Hockney
• Pro Euro Conservative Party: John Stevens
• Green Party: Hugo Charlton
• Official Monster Raving Loony Party: Alan "Howling Laud" Hope
• Democratic Party: Charles Burford
• Natural Law: Gerard Valente
• Campaign for Living Will Legislation: Dr Michael Irwin.