Mo Mowlam misled Tony Blair about the nature of her brain tumour before the Prime Minister appointed her Secretary of State for Northern Ireland in his government, it emerged last night.
A new film portrayal of one of the most popular figures of Mr Blair's time in office reveals that she kept the truth about her condition a secret for nine years.
Ms Mowlam, who died in 2005, was told in 1996 by her doctor that her brain tumour was malignant and that she had a life expectancy of three years. Yet she told Mr Blair, other Cabinet colleagues and her constituents, that it was benign.
Only her husband, Jon Norton, and her former doctor, the leading cancer specialist Mark Glaser, knew that her condition was terminal.
After Labour's 1997 landslide victory, Ms Mowlam was appointed Northern Ireland Secretary, in charge of the delicate peace process. She earned respect for her outspoken and frank manner, once telling the Reverend Ian Paisley, founder of the DUP, to "fuck off". The tumour affected her behaviour, her doctor said.
Dr Glaser, now chief of cancer services at Imperial College NHS Trust, agreed to talk to the writer of the Channel 4 drama, Mo, after obtaining permission from Mr Norton to waive patient confidentiality.
Mr Norton died last year. Dr Glaser revealed that he had ordered Ms Mowlam to tell Mr Blair the truth.
Dr Glaser told Neil McKay, author of the new drama starring Julie Walters to be broadcast on 31 January, that Ms Mowlam "deceived me" by not confronting the Prime Minister with the seriousness of her condition.
Dr Glaser told the writer: "A frontal-lobe tumour can cause disinhibition, behavioural disturbance and poor judgement. And there she was taking up a job in what was effectively a war situation.
"But there was nothing I could do. I was her doctor. I was responsible for her care, even if she wouldn't let me keep records in the proper places or write to her GP. I told her to tell Blair, but she didn't, she lied. So I went the extra mile for her because she demanded it from me. I was trapped... She was doing this very important job, one that affected so many people's lives, while she was ill; but she was also my patient and I owed her confidentiality."
Ms Mowlam battled with her condition, and its difficult treatment, while taking part in protracted and tiring peace talks.
Mr Blair sacked her in 1999, replacing her with Peter Mandelson. When she died in 2005, at the age of 55, it was claimed that she had had a fall at home and was moved to a hospice, masking the real cause of her death.
During the 1997 election campaign, Ms Mowlam revealed that she had been suffering from a "benign" tumour after one report likened her to a "slightly effeminate Geordie trucker". She said she had beaten the tumour, leading to newspaper headlines such as "Brave Mo has beaten tumour".