The Foreign Office has summoned China’s ambassador to the UK after a prominent British human rights activist was barred from Hong Kong, in a case that has sparked fears that the city’s autonomy is being eroded.

During a parliamentary debate, the MP Fiona Bruce, chair of the Conservative party’s human rights commission, asked what the Foreign Office was doing in response to shrinking freedoms in the former British colony.

She pointed to Benedict Rogers, deputy of the same commission, who was banned from entering Hong Kong earlier this month without reason. The Chinese government said his case was a matter of “foreign affairs” and accused him of planning to interfere in the territory’s politics.

“The Foreign Officedirector general for economic and global issues summoned the Chinese ambassador on this issue over the past few days,” said Mark Field, the minister of state for the Foreign Office.

“We have also made representations to Beijing, and I shall write to Carrie Lam in Hong Kong in the days ahead,” he added, referring to Hong Kong’s chief executive.

The case caused concern that Hong Kong’s autonomy was being further eroded. It also called into question the viability of the “one country, two systems” arrangement, the framework where the city manages the vast majority of its own affairs that was negotiated as part of the handover from the UK to China.

Rogers has long criticised China for tightening its grip on the city and was warned through an intermediary before his departure that Chinese authorities objected to his trip. He assured them it was a private visit, and that he would not be making an public appearances or visiting a trio of jailed democracy activists.

“I very much accept her position that we are very concerned that Ben Rogers, a UK national, was denied entry to Hong Kong on October 11, in absolute disregard of the ‘one country, two systems’ principle,” Field said.

The Commons Speaker, John Bercow, took the opportunity to commend Rogers for his work.

“Ben Rogers is an outstanding and articulate champion of freedom, democracy, human rights and the rule of law in Asia and elsewhere, well known to members on both sides of the house,” he said.

“[Rogers’] treatment was frankly utterly scandalous,” Bercow added. “Those responsible have certainly not heard the last of it, of that I think we can be sure.”

The following day prime minister Theresa May was also asked about the case, and pledged to maintain pressure on China.

“We want to ensure that the model of ‘one country and two systems’ is preserved and continues to operate,” May said. “On the specific case and the specific issue that she has raised, my right honourable friend the Foreign Secretary informs me that the Foreign Office has raised this issue at various levels in relation to Hong Kong and China, and we will continue to do so.”

Following Rogers being turned away at the border, Lam said the Chinese government could choose to bar anyone it wants from Hong Kong if it considered their presence in Hong Kong to be a matter for the foreign affairs department in Beijing.

At the time she refused to say if Chris Patten, the last British governor and current Oxford chancellor, would be barred the next time he attempted to visit.

A group of prominent lawyers from the UK, US and Australia said the rule of law in Hong Kong was under “serious threat” in an open letter this week.

“The independence of the judiciary, a pillar of Hong Kong, risks becoming a charade, at the beck and call of the Chinese Communist party,” the letter said.