Former Northern Ireland secretary Mo Mowlam is to make a scathing attack on the "vicious, violent and horrible behaviour" of her former cabinet colleagues.

The Observer reported on Sunday that Mowlam was set to make the claims in a Channel 4 documentary, in which she will also mount a devastating attack on the relationship between Gordon Brown and Tony Blair, and call for the chancellor to be moved to another job.

Mowlam, one of the most popular Labour figures and a darling of the grass roots, was sacked from the Northern Ireland Office in 1999, moving to the Cabinet Office before leaving parliament at the last election.

She says that a whispering campaign by senior figures was responsible for undermining her position in government.

Asked about reports that her illness with a brain tumour had affected her ability to do her job, she blames Labour's "spin machine".

"[That was] vicious, violent, appalling behaviour by the people that did it," she says in the documentary. "Some might say that's politics, I think its just despicable."

She said she confronted Alastair Campbell, Blair's powerful director of communications, who told her that "if I didn't talk about these problems they'd go away".

"Well, I'm sorry, but I didn't brief the press that I was going mad, that I was intellectually inferior since my brain tumour," she said.

But Number 10 said the accusations of briefings against Mowlam were "simply not true".

"These accusations have been made many times in the past, but no journalists have ever been able to say that Number 10 briefed against Mo, because it is simply not true," the prime minister's official spokesman told the Observer.

"It is very sad that she wishes to continue making these claims about a government of which she was a member and for which the prime minister believes she did a very good job."

Blair-Brown

Mowlam is also damning of the "destructive" relationship between Blair and Brown.

She says that during Cabinet meetings they would often fail to acknowledge each other's presence.

"That to me does not indicate a positive relationship. You could tell by the body language, by the amount of eye contact, how poor the relationship was. I just don't think that was helpful to government."

She blames their leadership rivalry for the poor relationship, saying she doesn't think Brown "ever got over" Blair taking the top job.

"If their relationship continues as destructively as it is now, I think the only way forward is for the prime minister to move him to another job," she said.