Mr Portillo, being lined up by the Tory right as a successor to the late Alan Clark's vacant Kensington and Chelsea seat,told reporters: "I had some homosexual experiences as a young person."
His comments were made on the back of persistent rumours about his sexuality while at Cambridge University in the early Seventies.
His candid revelations were contained in a two-month-old interview carried in The Times newspaper today. They are being interpreted by some as an attempt to clear any potential obstacles to his continued political rehabilitation.
Asked whether his homosexual experiences were sufficiently well known for people to have built other allegations around them, he told his interviewer: "I have no idea. I think people set out to spread the most damaging stories that they can think of."
Mr Portillo emerged from his London home with his wife, Carolyn Eadie, last night and said: "I was keen to put to rest the rumours that had been circulating about me and I cannot really believe that what happened a generation ago could be big news.
"I do not think it was a particularly big burden and I do not have any regrets. The truth is a good thing."
He said he had been "dogged by vicious rumours" recently and thought it was a good time to put the record straight.
The revelation came as Tory officials prepared to draw up a shortlist for the safe Kensington and Chelsea seat. Well over 100 people were reported to have declared an interest.
Harry Greenway, a former Conservative MP for Ealing North, who knows several leading Kensington and Chelsea Tories, said last night that the disclosures may have jeopardised Mr Portillo's chances of becoming the candidate.
Portillo's inheritance, page 5