China dismissed on Monday allegations of spying on the British Parliament after police arrested a parliamentary researcher on suspicion of spying for Beijing.

The arrest, made earlier this year but only made public this weekend, prompted Prime Minister Rishi Sunak to warn Premier Li Qiang in person about Chinese "interference" in democracy. The U.K. government also faced calls to get tougher with Beijing.

But it also provoked a strong denial in Beijing, risking further damage to ties already strained by criticism of China's human rights record against the Uyghur minority and the erosion of civil rights in Hong Kong.

House of Commons speaker Lindsay Hoyle is due to address lawmakers in parliament at 1:30 p.m. GMT, while Deputy Prime Minister Oliver Dowden is billed to give a "security update" afterward.

The spying claims, first disclosed in the Sunday Times, are likely to put pressure on Sunak's government to toughen its policy on China, as it seeks greater engagement with the Asian superpower.

Former Conservative party leader Iain Duncan Smith, who has been sanctioned by Beijing, branded the government's failure to label China a strategic threat as "weak."

"The result is that China is penetrating all our institutions from universities to parliament," he said.

But Business and Trade Secretary Kemi Badenoch said hardening the U.K.'s attitude could "escalate things," potentially scuppering U.K. hopes of getting China on board to help tackle vital global issues.

"China is the second largest economy in the world, it's heavily integrated in our economy as it is with many of our allies," she told BBC radio.

"We're taking the same approach that those countries are taking."

'Pure fabrication'

The suspect said to be in his 20s, was arrested at his home in Edinburgh in March, along with another man in his 30s.

Both were detained on suspicion of offenses under the Official Secrets Act and have been bailed until October.

If proven, it would represent one of the most serious breaches of security involving another state at the U.K.'s parliament.

Sunak said he confronted Li on the sidelines of the G-20 summit in New Delhi on Sunday, calling "any interference in our parliamentary democracy...obviously unacceptable."

Chinese Foreign Ministry spokeswoman Mao Ning, however, told a news conference in Beijing: "The so-called claim that China is conducting espionage activities against the U.K. is pure fabrication.

"China resolutely opposes this."

Mao added: "We urge the U.K. to stop spreading disinformation and stop its anti-China political manipulation and malicious slander."

The younger man who was detained has not been named by U.K. authorities. He has denied any involvement in espionage in a statement released by his lawyers.

"I feel forced to respond to the media accusations that I am a 'Chinese spy.' It is wrong that I should be obliged to make any form of public comment on the misreporting that has taken place," he said.

"However, given what has been reported, it is vital that it is known that I am completely innocent.

"I have spent my career to date trying to educate others about the challenges and threats presented by the Chinese Communist Party.

"To do what has been claimed against me in extravagant news reporting would be against everything I stand for."

Growing concerns

Concerns over China have been growing in the U.K. in recent years.

A report by British MPs last month branded Beijing "a threat to the U.K. and its interests," arguing that "the behavior of the Chinese Communist Party is currently characterized by increased aggression" toward Britain.

British security services last year warned MPs that a suspected Chinese spy had engaged in "political interference activities."

The woman, a London-based solicitor, reportedly donated 200,000 pounds ($275,000) to a leading opposition Labour MP and hundreds of thousands of pounds (dollars) to his party.

Britain in 2020 ordered the phased removal of Chinese telecoms company Huawei from its 5G network – including national intelligence – after pressure from backbenchers led by Duncan Smith, who called the firm an arm of the CCP.

In March, Chinese-owned video app TikTok was banned on British government devices over fears user data could be used or abused by Chinese officials.