The BBC has broadcast the recording of a 1998 Newsnight interview in which Lord Mandelson’s sexual orientation was mentioned.
The clip has never been repeated and hours after the original broadcast, BBC staff circulated a memo which said Lord Mandelson’s private life was not to be referred to.
The peer was originally outed in 1987 by the News of the World.
The recording of the 1998 conversation between gay journalist Matthew Parris and Newsnight presenter Jeremy Paxman was broadcast at the weekend.
In it, Mr Parris said that there were “two gay members of the Cabinet at least… Chris Smith is openly gay and Peter Mandelson is certainly gay”.
Mr Paxman replied: “Ah, I think we’ll just move on from there, I’m not quite sure where he is on that.”
The BBC memo said: “Under no circumstances whatsoever should allegations about the private life of Peter Mandelson be repeated or referred to on any broadcast.”
Lord Mandelson appeared on the Radio 4 programme Archive On 4 on Saturday to discuss his career.
On the Newsnight interview, he said: “What upset me first of all was that they should be debating this as though it was some sort of question that hadn’t been answered or that it was of some political importance.
“I had been outed by the News of the World some ten years before in 1987 and had long since got over it and got through it.
“What I didn’t accept very easily was this had suddenly become the subject of a political discussion on Newsnight, when in my view it had absolutely nothing whatsoever to do with my life as a politician or what I was doing as a minister.
“But even then I could have easily got over it I can assure you, until two hours later, after the programme had ended, there was a very aggressive knocking on the door by a journalist and when I didn’t answer the door, started bawling questions through the letterbox. And I just thought, I don’t need this, I don’t like this, I don’t approve of it and I just thought it was unacceptable journalism.
“I didn’t feel any inhibition leading my life as I did. To all intents and purposes – my home, my family, my friends – there was no sort of secret, nor was there any great fuss.”