And whether Mo is facing a room full of journalists or politicians, when the wig becomes too hot or uncomfortable, off it comes. "I'm going to take my hair off. I don't care about you lot," she told American reporters in the middle of a briefing before jetting off to Washington in May. She had just received her first attack from angry Unionists after warning that no one has a talks process veto.
"I'm in a mood. I've had a bad start to the day," she went on placing the wig on the table beside her to reveal the blonde fuzz growing back after the treatment. The gesture, made not for effect, is said nevertheless to both surprise and disarm even the hardest of Ulstermen.
Keeping up appearances has never been fundamental to Mo Mowlam's public persona. She carries off the difficulties and tensions in a style that is her own and that has barely changed since she was elected MP for Redcar in 1987. Even in the often frosty climate of the House of Commons, one former lobby correspondent recalls, she would often surprise colleagues and officials alike by tweaking her underwear and mumbling "bloody bra" or some such as she set off for the Ladies' to sort it out.
This forthrightness did not mean she lacked ambition: her left-wing politics changed along with the Labour Party and she has dubbed herself a chameleon who wants to be liked. As one of Tony Blair's earliest supporters, her New Labour credentials are impeccable.
Strange, then, that Mo has never quite looked the part. For New Labour has always been about image as much as content: rows of men and women in their immaculate suits looking ready for power. Mo was never an Indentikit politician: she was the woman who could change her tights on a train while having an indiscreet conversation with a Tory minister. Yet her allure has never been in doubt. The coverage of Mo visiting her Redcar constituency after she announced that she had had a brain tumour earlier this year owed more to Hello! than Hansard.
Not so long ago, another female politician showed that women could get to the top. It took effort, ability and above all willpower. She was prepared to change her voice, her clothes, even her hairstyle to project power. When Margaret Thatcher became leader of the Conservative Party, she had a light voice, curly hair and wore frocks, but she and her advisers stamped out her feminine side. Power dressing became the order of the day and the women making their way up the political ladder followed suit - one could not imagine Emma Nicholson or Edwina Currie without their hair any more than Mrs Thatcher, because their immaculate coiffeurs were part of their power. The only exception was Shirley Williams and she is remembered for taking the wrong train and her unpunctuality rather any of her achievements.
Now Mo Mowlam has changed the rules again. She is strong enough to feel secure in a personal style that is all her own and, with any luck, she might at last release many of the women coming after her from the straitjacket of the structured suit and immaculate hair.