Mo Mowlam, the former Northern Ireland Secretary who helped push through the Good Friday Agreement, was fighting for her life today in a London hospital.

The popular former Labour MP previously suffered a brain tumour and her increasingly frail appearance in recent months prompted fresh fears for her health. She was admitted to the King’s College Hospital at the weekend.

A hospital spokeswoman described her condition as still "critical but stable". It remained unclear as to whether her illness was a recurrence of the brain tumour.

The former MP for Redcar quit the Commons at the 2001 election after 14 years. She was made Northern Ireland Secretary when Labour swept to power in 1997 and quickly made a name for herself as a down-to-earth and often too honest politician.

Ms Mowlam, 55, won universal admiration for her perseverance in working towards the Good Friday peace agreement the following year. Her achievement was magnified by the fact that she was recovering from treatment for the brain tumour at the time.

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.

She took a particular political risk in 1998 by entering the infamous Maze Prison to speak with convicted 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Loyalist UDA/UFF prisoners had previously withdrawn their support.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. When she appeared alongside her replacement, Peter Mandelson, in 1999 many thought she had been made Health Secretary.

Instead, she was handed the Cabinet "enforcer" role and did a good job of hiding her disappointment. But her time in the post was marked by a steady flow of reports that someone in high places was "briefing against her".

There were also suggestions that Tony Blair had been irritated when the Labour Party conference gave her a longer standing ovation than him. The Prime Minister disputes this but there is no doubting that her searing honesty on everything from the Royal Family to her experimentation with cannabis upset party managers.

She became 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.

Ms Mowlam was born in Watford on September 18, 1949 and nearly died of pneumonia three months later. Her father was an alcoholic and the family were invariably short of cash.

They moved to Coventry where she attended Coundon Court Comprehensive School before going on to study at Durham and Iowa Universities. Ms Mowlam worked as a lecturer and university administrator before being elected MP for Redcar in 1987.

In 1995 she married Labour-supporting merchant banker Jon Norton, already a father of two.

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