London’s Metropolitan Police arrested more than 50 people on Saturday after protesters in Parliament Square displayed placards supporting Palestine Action, a group the UK government banned last month under anti-terrorism legislation. Officers moved in shortly after more than 100 demonstrators simultaneously revealed signs reading “I oppose genocide. I support Palestine Action,” detaining individuals on suspicion of breaching the proscription. A significant policing operation had been mounted in advance, and additional officers were brought in from outside forces. Palestine Action was proscribed on 12 July under the Terrorism Act 2000 following a series of high-profile break-ins and vandalism at defence sites, including £7 million of damage to RAF aircraft in June. The designation makes membership of, or public support for, the group a criminal offence punishable by up to 14 years in prison. Police had warned that anyone expressing backing for the organisation risked arrest. Saturday’s detentions come days after Palestine Action co-founder Huda Ammori secured permission from the High Court to challenge the ban, arguing it violates free-speech rights. According to the Metropolitan Police, more than 200 people across Britain have been arrested since the proscription took effect. The Westminster demonstration formed part of a wave of global pro-Palestinian rallies marking ten months of war in Gaza, with gatherings also reported in New York, Seoul and several European capitals. The Met said it expects further protests and counter-protests through the weekend and has advised participants to consider “the seriousness” of breaching the ban.