Franck Magennis of Garden Court Chambers was arrested in January while attending a picket in support of striking security guards at St George’s, University of London (SGUL).

At the time, he was working as head of legal for United Voices of the World (UVW), the grassroots union representing the workers.

According to Mr Magennis, he was arrested while “mid-conversation” with police officers who had threatened to arrest the workers and union officials under section 119 of the Criminal Justice and Immigration Act 2008.

Over £6,500 has been raised through a crowdfunding campaign in support of the legal action.

Susie Labinjoh, civil liberties lawyer at Hodge Jones & Allen, said: “Magennis’s arrest clearly raises important constitutional issues. We will be looking at all legal avenues to ensure that the police are held to account, that trade union members are not criminalised for going on strike, and that people are not arbitrarily arrested. The police must respect and uphold union members’ right to protest.”

Mr Magennis added: “This case is more important now than ever, as our society attempts to erode the lawful right to strike. The police have been emboldened by the anti-worker rhetoric of Boris Johnson’s Conservative government, who think they can act with impunity, putting workers’ rights and civil liberties at risk.

“By supporting our crowd funder, and standing up against my unlawful arrest, we send a message that this will not be tolerated. It is up to everyone to protect workers’ right to strike.”