Gordon Brown's closest allies spread lies about Sir John Major, the Leveson Inquiry heard today.
The ex-Conservative leader was so furious about false stories being briefed to the Press about him during Mr Brown's time as Chancellor and later Prime Minister that he wrote a letter to Downing Street complaining about the behaviour.
Sir John warned he would "go public" if the practice continued, the hearing was told.
He said there had been "a number of occasions" when he believed there had been briefings from people close to Mr Brown that were "totally dishonest and untrue and potentially damaging".
The first was in 2005 when he returned from a trip overseas to headlines claiming he, along with former Chancellor Norman Lamont, had blocked the release of papers relating to Black Wednesday.
That was "utterly untrue" and the pair were both "very angry", he said.
"For some reason of their own, the then Chancellor's advisers had briefed the Press that that was what we were doing."
The second occasion, which sparked the letter to then Cabinet Secretary Gus O'Donnell, now Lord O'Donnell. followed stories suggesting Sir John had made representations calling for Zimbabwe President Robert Mugabe's knighthood not to be withdrawn.
Mr Brown stripped the dictator of the honour in June 2008 in protest over human rights abuses.
Sir John was given the name of an adviser who had briefed the false claim, he said.
On June 30, 2008 he sent a letter to Lord O'Donnell.
It said: "This sorry episode raises, yet again, the extent to which those around Gordon Brown, both as Chancellor and now Prime Minister, are willing to lie - and I do not use that term lightly - to the media for party political advantage."