WHEN Betty Boothroyd announced earlier this year that she was quitting the Commons, she took the wind out of virtually everyone's sails.

When Mo Mowlam confirmed yesterday that she was throwing in the towel at the next General Election, there was barely a political eyebrow raised.

But then Madam Speaker had not spent almost two years plagued by whispers and rumours that she wasn't up to her Cabinet job and should be ditched by Tony Blair.

And Betty Boothroyd had not gone through the trauma of being diagnosed with a benign brain tumour in 1997.

So there was more than a touch of inevitability about Mo's decision to quit as Redcar MP after more than 13 years representing the constituency and more than three years in the Cabinet.

Mo is Labour's nearest thing to a film star and by far and away the most popular Cabinet Minister currently on show.

Who else, apart from US president Bill Clinton, could so nonchalantly get away with admitting she once smoked dope as a Durham University student, an admission made earlier this year as she settled into her Cabinet Office job co-ordinating the nation's attack on drugs?

And that celebrated spontaneous standing ovation at the 1998 Labour conference has gone down in party history not least for upstaging the Prime Minister who was speaking at the time.

Dr Marjorie (''call me Mo'') Mowlam was born on September 18, 1949. Her father, who died in 1981, was an alcoholic, but she remained close to her mother, who died last year.

Her early life was tough. She nearly died of pneumonia at the age of three months, and then her family, invariably short of cash, moved from Watford to Coventry, where she was brought up.

Once describing herself as ''rootless'', she said: "I like being a chameleon, getting on as well with City bankers as a roomful of bingo players.''

Dr Mowlam moved from Coventry to Durham, to Iowa and Florida, to Newcastle, Barnsley and then Redcar, where her attempts to get into Parliament achieved unexpected success. Only five days before the 1987 election deadline, the local MP decided to quit.

She arrived at Westminster, aged 38, to embark on a career which was to take her into the top echelons of Government.

After her first job as an assistant in the Shadow Northern Ireland Office, she became a spokeswoman on city and corporate affairs, where she took part in Labour's famous ''prawn cocktail'' charm offensive on the City.

Afterwards she took on Shadow posts on women's affairs, national heritage, and ultimately Northern Ireland.

She was diagnosed with the brain tumour shortly before the last General Election. Although it was operated on successfully, she was compelled for months to wear a wig which she detested. ''I hate the bloody things,'' she once said, ''and have to carry two around with me because I kept losing one.'' Once, she surprised people at an important meeting by suddenly whipping the hairpiece off her head.

But tough as old boots or not, few politicians could be expected to cope with a drip-drip feed of gossip against them especially in the aftermath of a very serious illness.

From her position as unassailable Labour darling of the post-election era and startling peace process successes as Northern Ireland Secretary, the "anti-Mo" briefings began.

Last year, she was removed from Ulster to make way for Hartlepool MP Peter Mandelson and given the broad but nebulous post of Cabinet Office Minister, a move widely seen as a humiliating demotion for Labour's most popular figure.

Once there, the whisperings intensified, not helped by Mo appearing on occasions not to have her heart in the Cabinet Office job.

Mr Mandelson, no close political ally of Mo, was suspected by some of fostering anti-Mowlam rumours but denied this as recently as last week.

The Redcar MP insists that she has not been defeated by the unknown whisperers. She took a "personal decision" to pursue interests outside Parliament and may go on to work in international affairs, conflict resolution and poverty.

But Dr Mowlam again hit out yesterday at the whispering campaign perpetrated against her. "The whispering has been going on for some time but it hasn't affected me," she said, insisting she still did not know who was behind the anti-briefings.

She added: "I don't think it was Number 10, I don't think it was Tony."

Earlier in a radio interview, her merchant banker husband Jon Norton remarked how some people actually dated the whispering campaign from the 1998 conference ovation. "I haven't personally been through the papers and looked to see...if that was the truth, but normally popularity isn't always the most popular thing among colleagues,'' he said.

Downing Street has insisted that in the meeting between Mr Blair and Dr Mowlam, neither of them mentioned stories of a briefing operation against Mo because such stories were "24 carat rubbish". But if yesterday's decision was inevitable, there is also a degree of confusion, not least over the timing of Mo's move. Over the weekend, her Redcar agent Keith Legg revealed that Mo had privately told her constituency party last May that she would spend the summer considering her future with an announcement likely in a few weeks.

And her Cabinet Office spokesman said she made the choice to quit during her holiday in Portugal which finished only on Sunday.

Dr Mowlam will be 51 later this month, an age when many politicians' careers are just taking off. So it was slightly odd to hear her remark in a BBC interview: "I've got a couple of years left before retirement." In her statement to the Press Association she claimed she had ''several years of my working life left''.

But last night, Dr Mowlam insisted she was in good health, describing herself as ''fine and dandy''.

Mo may not be quite the charismatic political phenomenon she was five years ago, but her office insisted that yesterday's decision had absolutely nothing to do with ill-health.

Yet more speculation on the Mowlam story will come next month with the publication of an unauthorised biography by journalist Julia Langdon - a book expected to point the finger at Mr Mandelson for some of the anti-Mo activity.

But the most exciting account - and one which Labour party managers may fear - will be Mo's own in an autobiography the MP is expected to publish after her departure from the Commons.

Tony Blair could well do without Mo's decision with the annual party conference just three weeks away.

But one thing's written in stone now - if you thought the 1998 ovation was something, just wait until she makes a farewell appearance as a Cabinet Minister this year.