Beijing has labelled as “malicious slander” and a “political farce” the scandal surrounding the arrest of a man in London on suspicion of spying for the Chinese government. On Sunday, it emerged that a parliamentary researcher with links to senior Conservatives and potential access to sensitive information had been arrested over allegations of spying for China. The man, who is in his 20s and was arrested in March with another person under the Official Secrets Act, is known to have held a parliamentary pass that allowed him unescorted access to large parts of the Westminster estate. On Sunday afternoon, China’s embassy in the UK published a short statement in response to media inquiries. “The claim that China is suspected of ‘stealing British intelligence’ is completely fabricated and nothing but malicious slander,” a spokesperson said. “We firmly oppose it and urge relevant parties in the UK to stop their anti-China political manipulation and stop putting on such self-staged political farce.” At a regular press conference on Monday, China’s ministry of foreign affairs was asked twice about the case and responded with similar language to the embassy statement. A spokesperson, Mao Ning, said: “The so-called Chinese espionage activity in the UK is non-existent.” On the sidelines of the G20 leaders’ summit in Delhi, Rishi Sunak said he had raised the matter with China’s premier, Li Qiang. The British prime minister said he told Li he had “very strong concerns about any interference in our parliamentary democracy”. According to the British account of the meeting, Li responded that the two countries had “differences in opinion”. The version of the meeting released by China did not mention the issue. State media said Li believed the two countries “should properly handle disagreements, respect each other’s core interests and major concerns”. State media have remained silent on the case. On Monday, however, the Ministry of State Security released new details of the life sentence delivered in May against a 78-year-old US man, John Shing Wan Leung, for espionage. No further details were given at the time. On Monday, the MSS said on its recently launched social media account that Leung, who had Hong Kong residency, had been a spy for more than 30 years after being recruited by US intelligence services in 1989. It claimed he monitored Chinese nationals and overseas Chinese in the US, would meet visiting Chinese personnel and report on them, and set up sexual entrapments “in an attempt to coerce and incite defection”. The fresh details were not explicitly linked to the British case but were reported extensively by Chinese state media in a potential message to the UK and allies about their own alleged espionage. China’s ministry of foreign affairs is scheduled to hold its daily press conference on Monday afternoon. The news emerged a week after Britain’s foreign secretary, James Cleverly, visited Beijing amid attempts to repair the bilateral relationship. Sunak is likely to face calls for an urgent question in the Commons on Monday about the scandal. MPs said there was a need to tighten the procedures for Westminster passes to be issued, with some expressing anger that the man had reportedly been able to work with a series of senior MPs, some of whom are now ministers, on foreign affairs issues, including relations with China. Some MPs have privately raised worries about the potential roles of Alicia Kearns, the Conservative MP who chairs the Commons foreign affairs committee, and Tom Tugendhat, the security minister. Both have taken a strong interest in China-related matters and are heavily critical of Beijing. The alleged spy is understood to have had contact with both of them, albeit only briefly in the case of Tugendhat, before he became a minister. Kearns declined to comment, adding: “While I recognise the public interest, we all have a duty to ensure any work of the authorities is not jeopardised.”