The former Northern Ireland Secretary Mo Mowlam is critically ill, hospital officials said tonight.

Dr Mowlam previously suffered a benign brain tumour, and famously sported a blond wig during talks to revive the Northern Ireland peace process, after cancer treatment caused her to lose her hair.

Her increasingly frail appearance in recent months have prompted fresh fears for her health.

The 55-year-old former MP for Redcar is at King’s College Hospital in London where a spokeswoman described her condition as "critical but stable". She did not disclose what Dr Mowlam was suffering from.

Christened Marjorie but universally known as Mo, the blunt-talking former university lecturer served as Northern Ireland secretary from 1997 - when her tumour was diagnosed - to 1999. She oversaw the negotiations that led to the Good Friday peace agreement and the creation of a devolved, power-sharing Government at Stormont.

Observers of the 22 months of negotiations said that her approachability was a key factor that made the agreement possible. Renowned for her light-hearted disregard of formality, kicking off her shoes and chewing gum at meetings, she is reputed to have removed her wig to break the tension during key meetings. And she reportedly called Sinn Fein’s Martin McGuinness "babe" during a phone conversation.

Although some Protestant politicians objected to her informality, her tenure appeared to encourage Sinn Fein to participate in the peace process.

She took a particular political risk in 1998 by entering the infamous Maze Prison to speak with convicted loyalist paramilitaries when it became clear the peace process needed their backing. Loyalist UDA/UFF prisoners had previously withdrawn their support. She spoke to the prisoners face-to-face for 60 minutes and two hours later the paramilitaries’ political representatives announced they were rejoining talks.

However, there was growing opposition towards her from more mainstream Unionists.

Despite her personal popularity on the left of the Labour Party, Dr Mowlam eventually fell out with Tony Blair’s centrist advisers. When she appeared alongside her replacement, Peter Mandelson, in 1999 many thought she had been made health secretary. Instead, she was handed the less high profile Cabinet "enforcer" role.

At the time she did a good job of hiding her disappointment. But her time in the post was marked by a steady flow of complaints that someone in high places was "briefing against her".

There were also suggestions that Mr Blair was irritated when the Labour Party conference gave her a longer standing ovation than him. The Prime Minister has disputed this, but few doubt that her searing honesty on everything from the Royal Family to her experimentation with cannabis upset party managers.

In her 2002 memoirs, Momentum, she said that she quit the Government and politics the previous year partly because Downing Street advisers were spreading rumours that her battle with the brain tumour had left her intellectually unfit.

She became was even more outspoken after she stood down as an MP, saying it was "harder and harder to defend what the Labour Government is doing".

"We have a Prime Minister who has thrown away the British constitution and seems to see himself as our president", she added.

She was born in Watford in September 1949 and grew up in Coventry. After studying social anthropology at the University of Durham, she gained a Masters and a PhD from the University of Iowa.

She was elected MP for Redcar in 1987. In 1995 she married Labour-supporting merchant banker Jon Norton, a father of two. They live in Redcar.

She has always preserved a zest for new challenges. Last year she set up a charity, MoMo, to help people in drug rehabilitation and the parents of disabled children. She was also appointed as agony aunt for the racy men's magazine, Zoo, and agreed to chair an attempt to set up a heavy metal music station in Belfast.

She has also worked for the charity Macmillan Cancer Relief.

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