The undercover police spy known until now as Officer A, who posed as an environmental activist for five years, can be named as Lynn Watson.
A useful member of an activist team for her driving and medical skills, Watson's real motives were revealed last October by the rogue officer Mark Kennedy when confronted by activists about his own identity.
Watson first surfaced in 2003 at a protest at Aldermaston, Britain's nuclear weapons centre. Watson claimed to be a care worker living in Bournemouth in Dorset. Her parents, she told friends, were from Glasgow but had moved to Slough, Berkshire, when she was young.
Using this story, or "legend" as it is known among police, Watson began to make friends among peace activists.
During 2004 she returned to Aldermaston women's peace camp. The following year, she moved to the student area of Leeds, West Yorkshire, where she became active in environmentalist groups centred around a radical social centre called the Common Place.
Watson also took a role in the UK Action Medics Collective, a group providing first aid at demonstrations. In common with other undercover officers, she could drive, offering another useful skill to a protest movement.
In 2007, Watson was arrested at the Department for Transport building in Whitehall, central London, during a demonstration against expansion of Heathrow. While other women glued themselves to the doors, she gave out leaflets, one activist claimed.
Watson disappeared from Leeds in early 2008, saying that she was leaving because she had met a man she wished to live with. She had a leaving party with close friends, but has not been seen by them since.
A Leeds University lecturer, Paul Chatterton, 37, a close friend, said she had "abused the trust" of activists and that her infiltration had been immoral. He saw Watson about twice a week, and regularly joined her in the pub or went running with her. "I considered her quite a close friend," he said.
Of medium height and with dark hair, Watson is well-remembered at the Common Place, a former pork pie factory in central Leeds which has given space and resources to radical groups for six years.
She was one of the original group who rented the redbrick premises, in Wharf Street. When the community centre was given a licence for drinks her membership card was number three. Volunteers working at the centre say she had "certainly been at the core".
Her credentials were not checked in a structure which was, and remains, open-minded and welcoming, like a smaller version of the base in Poland Street, off Oxford Street in London, which the Rowntree Trust provided in the 1970s for fledgling groups such as Friends of the Earth, the Low Pay Unit and the Campaign for Press and Broadcasting Freedom. Apart from hosting activist groups, the centre runs English classes for asylum-seekers, bike maintenance and repair workshops, and social events.
"If she was an undercover officer, I imagine she would have found us useful as a way of getting contacts more than anything else," said one of the volunteers, who all preferred not to be named.
Watson's abrupt disappearance in 2007 caused concern about her welfare rather than suspicion of her role.
"People were worried, though, when they tried to find out where she might have gone, and discovered that addresses and people she had mentioned did not exist," said a volunteer.
