UK Foreign Secretary Margaret Beckett was tricked by comic Rory Bremner when he pretended to be Chancellor Gordon Brown, the comedian has said.
He phoned her on the day of the 2005 general election, when she was environment secretary, and they discussed her Cabinet colleagues.
She gave frank assessments of some of them, advising "Gordon Brown" on who was performing well.
Mrs Beckett said she had "no recollection" of the conversation.
He described the conversation on BBC Sunday: "When she first took the call she said, 'Well, Gordon, and I wouldn't say this to anybody else...' and we suddenly realised what we were getting into, real stuff here."
She gave the impression that Tony Blair and Mr Brown were "putting together the Cabinet as a duo" after the election victory, Bremner recounted.
When Bremner, as Brown, suggested to her that the then-trade and industry secretary Patricia Hewitt was not up to the job, she allegedly said: "That's what a lot of people have been saying to me."
He also said she discussed former transport secretary Stephen Byers and ex-health secretary Alan Milburn, as well as describing what Bremner said was "factionalism" within Cabinet.
Bremner said the tape was never broadcast because of a "regulatory issue" but also because the impressionist wanted to "use Brown again in order to find out a little bit more about the Blair-Brown camps".
'Breach of privacy'
Mrs Beckett said: "I've never given my telephone number to Rory Bremner, nor knowingly had such a conversation with him, nor have I made a practice of discussing colleagues with journalists - other than in supportive terms.
"Perhaps Mr Bremner was aware of this when he chose to represent himself as a colleague - if indeed he did so.
"I have no recollection of a conversation in the terms that are being suggested. If he has done as he suggests, it is both an unprincipled and unpleasant breach of privacy."
Northern Ireland Secretary Peter Hain said he too had been rung by Bremner pretending to be Mr Brown, but had realised quite quickly that it was not the chancellor.
Bremner admitted he had slipped up with Mr Hain by getting some information wrong.
Mr Hain, appearing with Bremner on BBC One's Sunday, said: "I enjoy his impersonations, I think they're terrific, we all laugh like hell about them as we're all taken the mickey out of, but I do think, Rory, you should stop spreading cynicism and embitterment about politicians.
"Have a poke at us - great. But I've got my principles, I stick by them. I'm not questioning your honesty or your principles, but let's have a bit of fair play and a bit of give and take rather than all this cynicism".