Environment minister Jane Kennedy has quit the Government, saying she had been forced to do so because she would not give an assurance of loyalty to Prime Minister Gordon Brown.
The Liverpool Wavertree MP said she was unhappy with smears against Labour's own ministers emanating from 10 Downing Street, which she compared to the "bullying" of Labour activists by Militant on Merseyside in the 1980s.
But Ms Kennedy's version of events, in an interview on Sky News, was challenged by Downing Street, which said that Mr Brown had not demanded a loyalty pledge from her or any other minister.
Ms Kennedy made clear that the Prime Minister did not directly ask her for a pledge of loyalty and the decision to go was her own.
But she said it was made clear that she was expected to give assurances about her loyalty and told Sky News: "I wasn't able to give that assurance and so I have not been reappointed. That's the fact of what happened.
"I wasn't able to give that assurance because I have been unhappy for some time about smears against colleagues, about undermining of colleagues and friends by Number 10."
Asked whether that behaviour was from Mr Brown himself or those around him, she said: "I can't distinguish between the two and in my view it's how politics is driven forward by Gordon and the people around him. It really gets me very angry when I see that type of behaviour."
Ms Kennedy said she feared Mr Brown would lead Labour to its "bitter end".
"He himself has said in press conferences he had on Friday that he wants to fight on," she said. "My fear is that it will be to the bitter end of the Labour Party.
"I think we are now in such a serious position that we really are fighting for the future of the party."
