Pro democracy activists have called on Boris Johnson to end the “reign of terror” in Hong Kong after launching a hard-hitting campaign calling on Britain to “keep its promises” to the former colony.

A group of anonymous campaigners named Stand With Hong Kong has crowdfunded more than £320,000 in just 24 hours to put pressure on the new Prime Minister with a blitz of newspaper adverts, social media posts and a petition aimed at MPs.

Last month, Mr Johnson showed solidarity with the protesters, saying: “I do support them and I will happily speak up for them and back them every inch of the way.”

The campaign - which carries the slogan: 'Will Boris hold China to its promise on freedom for Hong Kong?' comes amid increasing concerns over Beijing’s influence in Hong Kong with the draconian Extradition Bill just one of a number of autocratic measures that campaigners say violates the Sino-British Joint Declaration.

The 1984 declaration, signed by former Prime Minister Margaret Thatcher and Chinese Premier Zhao Ziyang, guaranteed fundamental freedoms in Hong Kong for a period of 50 years after the end of British rule in 1997.