Hong Kong police made their first arrests under a new national security law imposed by Beijing, detaining protesters on Wednesday for carrying flags and signs calling for Hong Kong’s independence, as Britain accused China of a “clear and serious” breach of their handover agreement.

More than 300 protesters were arrested in total, nine under the new security law, as protesters took to the streets in defiance of the sweeping security legislation, which critics say is aimed at snuffing out dissent.