For once that truth-seeking missile Jeremy Paxman was not keen to know the truth. Parris has since been described as "sad and bitter" because he could not be openly gay and an MP. This is absolute rubbish as Parris has far more influence now through the media than he ever would have had as a backbencher. What's more the manner in which Parris talked about Mandelson was not so much a militant outing as the kind of conversation that is had by the media, by lobby correspondents, around certain dinner tables every day of the week. Parris presumed to know and presumed that everyone else knew too. This is the way that Mandelson's sexuality has long been discussed.
This position, half in and half out of the closet, is far harder to understand and I should imagine more stressful to live with than either keeping the closet door firmly shut or declaring oneself openly gay. It certainly causes a lot of muddle-headed thinking. For a start there is the terminology itself. How many times I wonder can you be outed and still be In?
Three strikes and you're clearly not out. Mandelson has so far been outed by the News of the World, by Brian Gould, by Edwina Currie, by Oliver James, by The Sun and yet he cannot properly be described as out because he will not utter those precious three words "Yes, I am".
Even more farcical than this, however, people are now turning themselves inside out to tell us that this minister's sexuality is none of our business. "Outing" per se is frowned upon by everyone as something distasteful that only militant homosexual groups led by the likes of Peter Tatchell get up to. I also find this laughable as half the business these days of the popular press involves some sort of "outing". Public figures even in the form of B-list celebrities are hounded until they admit that they are gay or have taken drugs or have a mistress or eating disorder. This, of course, is not called outing but investigative journalism.
The liberal press on the other hand dislikes outing because it maintains it is a gross invasion of privacy. There are many things wrong with outing yet no one seems prepared to put the whole issue into any kind of context. The phenomenon of outing was largely a response to the Aids epidemic. The activist slogan "Silence = Death" was taken literally. It was considered important that the public knew that certain public figures were gay so that homosexuals could not be so easily marginalised.
The process of coming out has become a gay passage of rites, something that heterosexuals never have to got through. It still requires immense bravery and all sorts of people are still rejected by their families and colleagues just because they decide to tell the truth about their sexuality.
Many who profess a belief in equality say that this is a little more information than they need or they complain about the flaunting of homosexuality because they take for granted the heterosexual privilege whereby heterosexuality appears transparent because it is everywhere around us. No one accuses straight people of parading their heterosexuality but that is exactly what happens all the time so that while heterosexuality is public, homosexuality is still seen as an essentially private affair.
While we may congratulate ourselves on more liberal attitudes to homosexuality - and indeed The Sun has made a vast leap forward this week - we should also ask ourselves how such changes come about. Straight people, even those who work at The Sun, do not just turn from raving homophobes to caring, sharing, live-and-let-live liberals overnight do they? No. Prejudice turns to tolerance because many have struggled long and hard to change our perceptions.
All those, over years, who have campaigned for gay rights, for an end to discrimination at work, for equality of the age of consent, all those who have sat up half the night counselling suicidal gay teenagers, or those who have confronted queerbashers, in fact all those ordinary gay people who despite the difficulties have not hidden their sexuality, even if it meant having to leave their homes and families, these are the people who have made a difference.
So too have the public figures who have one by one come out and then gone back to work. We now live in a culture where Lily Savage and Dale Winton are hosts of our most mainstream shows, where camp is an aesthetic that dominates even children's TV, where the reaction to an announcement of same-sex preference is often "We already knew" or "So what?"
Indeed, if Mandelson told us what we already presume to know, the response would be a huge So what? Yet his refusal to come out in some way places him above the struggle. To reap the benefits of a more open society without being open yourself does strike me as somewhat hypocritical. As a master manipulator one feels that this is a case where he has actually mis-read the signals, and that even for a politician honesty may indeed be the best policy.
The counter-argument - that heterosexuals do not have to discuss their private lives so nor should gay people - no longer holds up. At every available photo-opportunity Tony Blair flaunts his sexual preference, shoving his heterosexuality down our throats with pictures of Cherie and the kids. Indeed both William Hague and Gordon Brown have had to quash the rumours about them with visual evidence of heterosexual desire in the shapely forms of Ffion and Sarah.
On the whole, though, we don't really mind what kind of sex public figures have as long as they have it. We are far more perturbed by those who present themselves as asexual such as Ted Heath and Ann Widdecombe. Now if Peter Mandelson were to announce to the world that he really couldn't be bothered with sex of any kind that would be newsworthy.
Yet I cannot say, as others have, that Mandelson would be personally happier if he came out. I cannot say that "the gay community", whatever that is, would embrace him. I cannot say that despite a more tolerant climate some would not say and do nasty things. All I can say for sure is that by not coming out he is not keeping his private life private but he is in fact provoking an extraordinary amount of interest in it.
Matthew Parris has been called "attention-seeking" by Downing Street, yet I can think of no better way of getting attention than Mandelson's strategy of avoiding the issue. If homosexuality were truly accepted then this would be fine - his private life would be private - but we are some way off from that. He is acting as if equality has already been achieved, but it hasn't and nor will it be until there is no shame and stigma attached to being gay.
He is a powerful man who could do much towards ending discrimination on the grounds of sexual orientation simply by being honest. That surely would be in the public interest as well as his own because then he could truly left to be get on with his private life.