She is slight, quiet, and unassumingly pretty. Matilda Gifford appears an unlikely whistleblower on an alleged covert counter-intelligence ring operating in Strathclyde Police.

The 24-year-old activist with anti-airport protest group Plane Stupid says she found herself the focus of an attempt by members of Scotland's largest police force to infiltrate her organisation and, after recording her conversations with officers, made the decision to go public.

The resulting press and political attention has come as a shock for the student. Articulate, bilingual, and fiercely sharp, Ms Gifford has had to hit the ground running in order to deal with a sudden and copious press interest in her story.

With support from her Plane Stupid colleagues, Ms Gifford has been interviewed by both domestic and international newspapers and repeatedly appeared on television news since the story broke on Friday and was reported in The Herald on Saturday.

Ms Gifford says initially she was nervous of speaking to reporters. "I had no idea how I would be received, whether the press and the public would be sympathetic.

"I'm not involved in this cause to be popular and I know that we are regarded with suspicion and generally disliked. The response has been amazing though. I was initially very, very guarded with the press and very nervous, but now the story is out I just feel relief."

Dan Glass, the Scotland convener of Plane Stupid, says he and members of the group are impressed with the way Ms Gifford has conducted herself.

"Tilly has done amazingly well. She wouldn't admit it, but she has been very brave in speaking out. We would hope now that we have created a platform where people who have been approached in similar ways by the police will be able to come forward also."

Ms Gifford was born in London. At the age of seven, she moved with her family to the north of France. She and her parents settled in the tiny hamlet of Saint Remy au Bois, population 100, where the family set up an organic jam-making company.

Aged 19, she decided to study in Scotland, starting at Glasgow University. Come second year, she had been offered a place at the Glasgow School of Art and switched degrees. To support herself, she now works part-time as a chef and on an organic farm.

Ms Gifford speaks with the quiet authority of the truly passionate. Climate change had held a terror for her for a number of years before she decided, in February last year, to become involved in Plane Stupid.

The ethos of the group appealed so strongly, she opted to take a gap year from her degree and immerse herself in volunteering with Plane Speaking, a group committed to helping residents living under the flight paths of Scottish airports.

Ms Gifford is still adapting to the shift from art student to "espionage target". Her story reads like a television plot. It began when she took part in much-publicised campaigns against the expansion of Scottish airports, and was charged with vandalism and breach of the peace after a protest at Aberdeen airport on March 3.

On March 22, she was arrested again, inside a derelict building she and her friends were assessing its potential as an art exhibition space.

Her belongings were confiscated, but when they were returned to her, her house keys were missing.

She complained and, three days later, she says, she was invited to Partick police station to collect her keys. The invitation was written on Strathclyde Police headed notepaper, but hand-delivered in a plain envelope.

Arriving at the police station, Ms Gifford says she was ushered into a back room and asked if she could spend a quick 20 minutes talking about the action group. Feeling that the question was not simply a request, she agreed to talk.

During this meeting and another, five weeks later, the 24-year-old used her mobile phone to record conversations with the officers, during which she says she was offered cash to divulge information about Plane Stupid's inner workings, and told a criminal record would hamper future attempts to find a job.

Ms Gifford describes feeling perturbed by the first meeting but also elated; here, finally, was proof that police were targeting the group.

"After discussing it with the other Plane Stupid members, we realised this was a chance to gain hard evidence of the intimidatory tactics of police, and the way they are trying to prevent people taking action on and asking questions about climate change," she said.

On Tuesday last week, Ms Gifford says she met the officers for a second time in a west end cafe. This time, however, she had back-up from Plane Stupid activists Dan Glass, 25, and Juliana Napier, 24, who recorded the meeting via devices sewn into Ms Gifford's clothing.

It is claimed that officers ushered Ms Gifford to a car and drove her to Morrisons supermarket cafe in Anniesland where they offered her money, tax-free, in exchange for weekly meetings.

The relationship with police ended last Thursday morning when Ms Gifford appeared at a planned meeting accompanied by her lawyer, Patrick Campbell. After waiting for half an hour for the men to show, Mr Campbell left.

Ms Gifford claims she was followed as she walked to a friend's flat and approached by the officers when alone. The men expressed their disappointment that Ms Gifford had contacted a lawyer and she has heard nothing from them since. When Plane Stupid and Mr Campbell attempted to contact the officers at Strathclyde Police's main headquarters, their names were not available at the main switchboard.

Since Ms Gifford went public with her experience, there have been other claims that police have tried on several occasions to infiltrate Plane Stupid, which, according to Ms Gifford and Mr Glass, raises worrying questions of how taxpayers' money is being used to investigate groups that are committed to non-violence.

Also of concern for Plane Stupid is that Ms Gifford is the first to come forward. Its leaders question whether others have felt so intimidated or isolated by police that they have been too afraid to speak out.

Strathclyde Police will say relatively little. Assistant Chief Constable George Hamilton said: "Officers from Strathclyde Police have been in contact with a number of protesters involved with the Plane Stupid protests, including Aberdeen Airport. The purpose of this has been to ensure any future protest activity is carried out within the law."

Ms Gifford says that for the first few days after her final meeting with police, she was frightened to go home, and was fearful she was being watched. Now her face is familiar to anyone picking up a newspaper, she says that fear has passed.

"What we are doing is questioning the tools of the state and questioning how taxpayers' money is being spent. What drew me to return to live in Britain was the fact that it is possible to speak out, it is possible to start necessary dialogue, and know that there are mechanisms in place to allow you to do that.

"I am more afraid of the outcomes of climate change than I am of the police. I will continue to do what I do and be inspired."