The police were enforcing the Police Reform and Social Responsibility Act which bans people from setting up camp in Parliament Square. Protesters had come armed with gear to set up an overnight camp which is illegal. Jenny Jones says she had joined the protesters to investigate claims of disproportionate police response to the illegal protest. She was dearrested after giving her details for a summons and could now be prosecuted.
Former leader of the Green Party and their only MP, Caroline Lucas, was arrested last year for public order offences at an anti-fracking protest and Nigel Farage was assaulted in Brighton at an anti-democracy protest organised by left wing extremists, including Green Party councillor Ian Driver. It seems that the Green Party think that laws are only there for other people,