Amnesty International called the mass arrests “deeply concerning”.

“The protesters in Parliament Square were not inciting violence and it is entirely disproportionate to the point of absurdity to be treating them as terrorists,” said Sacha Deshmukh, the organisation’s chief executive.

“We have long criticised UK terrorism law for being excessively broad and vaguely worded and a threat to freedom of expression. These arrests demonstrate that our concerns were justified.”