Hong Kong Chinese people should be given British citizenship to reassure them amid increasingly violent clashes between protesters and police in the city, a senior Tory MP has said.

Tom Tugendhat, who chairs the Commons foreign affairs committee, said Britain should have extended the right when it gave up colonial control of Hong Kong to China in 1997.

It comes as protesters, some waving union jack flags, demand that Hong Kong leader Carrie Lam steps down and scraps legislation that could have seen criminal suspects sent to mainland China to face torture and unfair or politically charged trials.

Demonstrators say they are fighting the erosion of the “one country, two systems” arrangement enshrining some autonomy for Hong Kong when China took it back from Britain.

But China has begun to characterise the protests as something approaching “terrorism” while amassing paramilitary police, just over the border from the city on the mainland, prompting fears of escalation.

In a series of tweets, Tugendhat described the police movements in the Chinese city of Shenzhen as “worrying” and said “one country, two systems” was “under threat”. 

He said the UK has obligations under the agreement which gives Hong Kong special status until 2047 – 50 years after reunification with China – including “extending full citizenship rights” to Hong Kong Chinese.

“This should have been done in 1997 and is a wrong that needs correcting,” he said. 

Britain should also join with international partners to make clear that the joint declaration agreement which handed over Hong Kong was lodged with the UN, giving it more weight than a simple bilateral agreement between the UK and China, Tugendhat said.

He said China should be urged not to send in mainland forces while protesters to end the protest and seek political solutions to the current problems.

Alongside other measures this “would show the world is concerned and recognises the rights both of the Hong Kong people and Beijing under existing treaties”.

He added: “Ending violence and finding a political solution is the only answer. We should do what we can to help.”

This week, the protests escalated dramatically as thousands of people closed down Hong Kong airport, one of the busiest in the world, and forced the cancellation of hundreds of flights.

Police have arrested more than 700 protesters since early June and say they have infiltrated the ranks of the demonstrators, leading to concerns that officers were inciting violence.

Scores of people have been injured, both protesters and police, including a woman reported to have had an eye ruptured by a beanbag round fired by police during clashes on Sunday.

Police said they are investigating the incident, which protesters have taken up as a rallying cry.

Meanwhile, China is amassing paramilitary police across the border in Shenzhen for exercises in what some saw as a threat to increase force brought against the mostly young protesters who have turned out in their thousands over the past 10 weeks.

Hong Kong olice have meanwhile demonstrated water cannon, and a Chinese official has said “sprouts of terrorism” were emerging in Hong Kong, prompting fears that Beijing may be paving the way to use anti-terror laws to restrain the protesters.