UK Prime Minister Rishi Sunak on Sunday told premier Li Qiang that he had "very strong concerns" about China's "interference" in democracy following the arrest of a parliamentary researcher for spying.
"I raised a range of different concerns that we have in areas of disagreement, and in particular, my very strong concerns about any interference in our parliamentary democracy, which is obviously unacceptable," Sunak told British broadcasters of his meeting with Li on the margins of the G20 summit in India.
"The right thing to do is take the opportunity to engage to raise concerns specifically, rather than just shouting from the sidelines," he added.
Li said that both countries should refrain from mixing trade and economic cooperation with politics and security, according to Chinese state news agency Xinhua.
UK police said Saturday that they had arrested a man in his twenties at his home in Edinburgh for spying, with the Sunday Times reporting he was a researcher in Britain's parliament.
Officers from the Metropolitan Police Service arrested him, and another man in his thirties, in March on suspicion of offences under the Official Secrets Act and both have been bailed until October.
The Sunday Times said the suspect in his twenties had contacts with MPs from the ruling Conservative Party while working as a parliamentary researcher.
They included Security Minister Tom Tugendhat and Alicia Kearns, the chair of the Commons foreign affairs committee. Tugendhat is reported to have only had limited contact with the suspect, and none while security minister.
- 'Epoch defining' -
The suspect is a Briton who has worked on international policy, including relations with Beijing, and previously worked in China, the paper added.
If proven, it would represent one of the most serious breaches of security involving a hostile state at the UK's parliament.
Domestic intelligence service MI5 last year warned that a female Chinese government agent called Christine Lee had been "engaged in political interference activities on behalf of the Chinese Communist Party, engaging with members here at parliament".
In July the Commons intelligence and security committee claimed that China was targeting the UK "prolifically and aggressively" and that the government did not have the "resources, expertise or knowledge" to deal with it.
Justice Secretary Alex Chalk told Sky News on Sunday that Sunak "has been very clear when it comes to China, it is an epoch-defining... challenge... so of course we have got to take it extremely seriously.
"I know that the police and no doubt other agencies will take it as seriously as well, and let's learn whatever lessons need to be learned," he added, when asked if the system for handing out parliamentary passes may be reassessed.
Despite the allegations, Sunak defended last month's visit to Beijing by his foreign minister James Cleverly.
"If you look at how countries like America, Japan, Canada all engage with China, that's what they do, because engaging with people allows you to raise concerns directly," he said.
"I think that's a more powerful thing to do."