China’s foreign ministry said on Tuesday its diplomatic missions abroad have the right to “take necessary measures” to maintain security after the British police opened an investigation into the assault of a Hong Kong protester who alleged he was dragged into the Chinese consulate in Manchester and beaten up during a demonstration.

Britain’s foreign secretary summoned the charge d’affaires at the Chinese embassy in London on Tuesday to express the UK’s “deep concern” about the assault allegations and to demand an explanation for the actions of the Chinese consulate staff.

Manchester police said a peaceful protest outside the Chinese consulate on Sunday turned into a “hostile” situation when unidentified men came out of the building, dragged one of the protesters into the consulate grounds and assaulted him. Police said officers had to intervene and remove the man.

The man, who is in his 30s, told reporters that he was beaten up when protesters tried to stop the masked men from tearing down their anti-government placards outside the gates of the consulate. The protesters had gathered at the consulate as the Chinese Communist Party opened its week-long congress in Beijing on Sunday.

Chinese foreign ministry spokesman Wang Wenbin rejected the accounts of the protester and Manchester police, telling reporters on Tuesday that the protester had “illegally entered” the consulate and “jeopardised the security of the Chinese diplomatic premises”.

“The diplomatic missions of all countries have the right to take necessary measures to maintain the peace and dignity of the premises,” Wang said in Beijing. “What I want to stress is that the peace and dignity of Chinese embassies and consulates abroad must not be violated.”

He added that the British government should step up protection for Chinese diplomatic posts and personnel in the UK.

Downing Street said the incident was “deeply concerning”, and UK MPs pressed the British government to take tougher action during an urgent questions session in Parliament on Tuesday.

Video on the BBC website showed a scuffle breaking out in front of the consulate after masked men tore down and took away the protesters’ placards. The video appeared to show several men wearing face masks beating up someone who had been pushed to the ground amid the clashes. Police said the protester was taken to a hospital to treat his injuries. No arrests have been made.