CPS used joint enterprise principle, usually reserved for gang crime, in the case of Lisa McKenzie, who was cleared of all charges

Legal experts have criticised the prosecution of a protester who was arrested when a fellow activist placed a sticker on a window of a block of luxury flats.

The incident has raised concerns that the police are targeting known protesters for prosecution, even if they are non-violent, using joint enterprise laws.

Lisa McKenzie, a research fellow at the London School of Economics, was accused of assisting an unknown person to put the sticker on a window to protest against “poor doors” – separate entrances for social housing tenants in upmarket blocks that also cater for private tenants.

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After she was found not guilty at Stratford magistrates court - the judge ruled there was no evidence against her - McKenzie said she had been picked out by police.

“The police were asked how they knew it was me and how they knew my name, and they said that I had been profiled in the meetings earlier, and the judge said he was very, very uncomfortable with how I had been profiled,” she told the Guardian.

Joint enterprise means a person may be found guilty for another person’s crime if it is judged that they shared a common purpose. It is more commonly used in connection to gang violence.

McKenzie’s barrister, Ian Brownhill, who has previously represented a number of Occupy protesters, said it was “dangerous because, in terms of joint enterprise, if you are joined together in a single purpose – of course you are, in a large demonstration – and part of it turns disorderly, then they can try and hold you responsible”.

Facebook Twitter Pinterest Lisa McKenzie celebrates at the Salmon and Ball in Bethnal Green with friends. Photograph: Linda Nylind/The Guardian

“What they have done in this case is they have picked out Lisa and said Lisa is responsible for everything that crowd of protesters has done,” he added.

Leading lawyers and campaigners have criticised the case being brought to court by the police and the Crown Prosecution Service.

“This whole case smacks of overkill by the prosecutors,” said Mike Schwartz, a solicitor and expert in protest law. “It is questionable whether she should have been profiled, and prosecuted in the first place. And to have had the joint enterprise legal principle – most commonly used in drug and gang violence cases in the Old Bailey – wheeled out against her; fortunately, the judge had the wisdom to see what was going on. But the police and prosecutors must learn the lessons before cases get off the ground.”

Tom Wainwright, a barrister and author of The Protest Handbook, said the case appeared to fail the CPS test on both the likelihood of success and the public interest. “There was clearly never any prospect of a conviction,” he said. “Was it really necessary to take this to court?

“These prosecutions are indirectly affecting the right to protest, because even if there is no conviction people are restricted from protesting by bail conditions, and have a criminal trial hanging over their heads for months.”

Wainwright’s co-author and fellow barrister Anna Morris was one of several human rights lawyers to draw a comparison with the case of the seasoned peaceful protester John Catt. The 90-year-old, from Brighton, challenged the retention of his data on the national domestic extremism database – kept despite him never having been involved in any criminality. His case, dismissed by the supreme court, will now be heard in Strasbourg.

“Many protesters feel that their profiling and data retention is of itself a form of guilt by association,” she said. “The use of joint enterprise principles, more usually seen in murder charges, are controversial. In relation to public protest, their use may represent a change in strategy being deployed by the police and prosecuting authorities to pursue criminal charges against peaceful protesters.”

McKenzie’s arrest came after she took part in a protest organised by the anarchist group Class War on 19 February outside One Commercial Street, a 21-storey block of flats in east London.

Prosecutors alleged that one demonstrator caused £50 worth of damage by sticking a sticker to a window, although it was accepted that McKenzie did not stick it there herself.

The district judge, Richard Hawgood, ruled that McKenzie had no case to answer on a charge of using threatening words or behaviour, on which the prosecution had also given evidence. He found her not guilty of criminal damage.

Kevin Blowe, coordinator of the policing pressure group Netpol, said he expected to see further police interest in groups protesting the housing crisis, such as Class War.

“We’ve seen evidence that police are very keen to establish links between groups who are active on this issue and whether they are likely to grow,” he said, adding that his group had advised those attending the student demonstration on 4 November to cover their faces in order to draw attention to the privacy rights of activists.

The CPS has been approached for comment.

