That her tenure as Secretary of State for Northern Ireland is seen as radical tells us more about Britain than it does about her own manner or modus operandi. Unlike all of her predecessors she refused to be sequestered in Hillsborough Castle, bugged and bunkered in paranoid seclusion and briefed by a bureaucracy which enjoyed unlimited power without responsibility. She took up her posting in 1997 as the herald of a new era, bearing the promise of a new historic settlement. But the confidence of a government that no longer needed to look over its shoulder, that no longer needed the Ulster Unionists to preserve its own power - if not theirs - did not necessarily augur such a stiff challenge to Stormont's culture.
Anywhere else she would not have generated either the piquancy or petulance that ricochets around her. It is unthinkable that any other constituency would refuse to do business with Her Majesty's mandate, and describe her - as the senior Unionist John Taylor did recently - as little more than a barmaid. But in Northern Ireland she had only to be more or less normal to disturb the brittle protocols of the most patriarchal place in these islands. She had only to behave as if she represented all of the people to be pilloried for being a Provo sympathiser.
"There is nothing in her actions or arguments that could be regarded as anti-Unionist or pro-Republican," Inez McCormack, president of the Irish Congress of Trade Unions, has said. But the Unionists' rude reluctance to do business with her exposes their own spectacular sectarianism. "They could deal with their colonial master, but not their colonial mistress," said McCormack.
That, plus visceral paranoia, has made her reign an original one. From the perspective of the Republic (not the most radical place) she seems revolutionary. For a start she knew the territory. She has been visiting the place since the 1980s, and she has networked energetically, meeting anyone from trade unionists to feminists to loyalists to grieving families. Everyone knew they were dealing with someone different, because she was the first who was not a prisoner. Previous secretaries of state hunkered down in their splendid castle, taking tea with the great and the good, and inviting counsel from a Secret Service masquerading as a Civil Service. They were trapped and fearful, beholden to the security apparatus and that species of unionism which regarded secretaries of state as men with a duty to preserve a one-party state purged of Catholics.
That was the way it worked until 1997. What made the new order so extraordinary was that Mowlam brought both style and substance to the peace project. Her vaunted reputation as a raunchy buffoon, good at burping and swearing but bad at syntax, good at hugging but bad on detail, veiled a tactical intelligence and a knowing woman. She was more typical of her times than the bowler-hatted gents with whom she had to do business. But her style is also more controversial and strategic than often even her critics would credit.
She makes people feel they have had, however briefly, her attention. She has met the family of the murdered lawyer Pat Finucane and Robert Hamill, a young Catholic kicked to death under the inert scrutiny of the RUC in David Trimble's constituency - a gesture unthinkable in the old days. Not surprisingly, this engenders a mixture of relief and suspicion. "She uses her skills to make you feel she is listening, that she is nice, but you wonder whether she uses these skills to manage you rather than address your concerns," says one human rights lobbyist.
Some seasoned movers and shakers reckon that the new tone would have arrived anyway with New Labour. Nonetheless we cannot overestimate the impact of a secretary of state who goes into the ghettos and delivers dignity and respect. "You see people going to a meeting with Mo who have never had access to that level before. They expect a colonial attitude and what they get is touchy feely - and all she has done is treat them like human beings. That is a big cultural change, and is partly a product of the peace process itself," says one legal advocate.
Her style is everything to do with her gender and her generation, and also the personal troubles about which she has been so candid and modest. There was massive sympathy for her in the aftermath of her brain tumour. "Ordinary men and women responded passionately to her attitude, to her looks, her hair, her weight," said McCormack. "Instead of expressing terror about what was happening to the body by masking it, she tackled the terror, she took off the wig!"
British politics had never known anyone like this - a woman made big and bald by steroids and cottage pie. And anyone who has spent time with Mowlam and her husband, Jon Norton, a socialist merchant banker who also happens to be a handsome and sweet man, is witness to adoration, desire and joie de vivre. Quite a challenge.
Many feminists regard the endless comments on her touchy-feely approach as a serious misreading. McCormack, one of the few powerful women in Northern Ireland, said: "She links it to getting things done. Her style is not about dominance; it moves from a co-operative mentality to a dealer mentality. She is a pragmatist, committed to a way of doing business that is about co-operation and consensus and it resonates with the Good Friday Agreement - it is about creating a culture of co-operation."
What has been exposed, however, is that Ulster Unionism does not co-exist with co-operation. That is Northern Ireland's problem.
Mowlam's patient, calming encouragement of confidence in politics as a process that can deliver change to a brutalised society is still seen by some as weakness, and by others as pro-Republicanism. Only in the interregnum between the Good Friday Agreement and its implementation has mainland Britain been finally confronted by the meaning and motives of unionism, the autocracy of the Northern Ireland office, and the awesome resources of the security state.
No sooner was the ink dry than civil servants began rewriting the agreement, particularly the equality section - little aired on the mainland - which uniquely inscribes the principle of parity into the practice of government itself.
When Mowlam was persuaded of the problem last summer she deputed the diligent Paul Murphy, now Welsh Secretary, to deal with the detail. It took many gruelling months to reinstate the wording of the agreement into the legislation put before the House of Commons.
Mowlam has been careful in her dealings with the security machine and the Stormont state - some would say this has left her weak and victimised. It took overwhelming evidence before she was prepared to persuade the Cabinet to order an inquiry into Bloody Sunday. And there is still no progress on the murder of Robert Hamill or his solicitor, Rosemary Nelson. Their deaths have aroused more interest and outrage in the US Congress than the British Parliament.
Mowlam also circulated the Human Rights Watch dossier on the murder of Pat Finucane, allegedly involving a security services collusion. The dossier named names. Mowlam gave it to RUC Chief Constable Ronnie Flanagan - who has so far failed to deliver justice to the Finucane family - and called in British top cop John Stevens to resume his investigations. There were swift arrests. But there was no public inquiry into this long-running and lethal story. The arrests guaranteed that an inquiry is bounced far into the future.
Mo Mowlam's story tells us something significant about power - gender power and colonial power. Here is a woman, ambitious, strategic, and every inch a professional politician (even a calculating one, as last week's events showed). But because she is a woman she is always scrutinised for a confirmation or transgression of femininity.
Surviving a disastrous childhood, a brain tumour or Mandelsonian malice, she can be ruthless. As the recent negotiations reached their climax, her Prime Minister marginalised her and allowed the Unionists to treat Her Majesty's mandate with contempt. She is not the first woman to be locked in the stocks by this government, and subjected to public humiliation. But this summer will show us if he and she can grasp what some British politicians will eventually have to do: take responsibility for unionism, look it in the eye and tell it that there is no alternative to democratic co-operation, to breathing the same air as Catholics. She has to confront unionism with its history and - like South Africa's Boer rump - encourage it to be relieved of the burden of its past.
Her Prime Minister has failed to deliver this so far, and she herself has only just hinted at it. Now is the time when her intelligence, ruthlessness and humanity will be truly tested.