British intelligence services are poised to unmask a number of Chinese spies in the coming months amid concern that a network of operatives is operating in Westminster.

Whitehall sources said suspected foreign spies working in the Commons face being detained under new espionage laws after a parliamentary researcher was arrested on suspicion of spying for China.

The British citizen, in his late 20s, has worked with senior Conservative MPs who have access to highly sensitive or classified material, including Tom Tugendhat, the security minister, and Alicia Kearns, who chairs the foreign affairs select committee.

He was arrested in March alongside a second man, in his 30s, thought to be a university academic. Both have been released on bail.

After news of the arrest broke on Sunday, Rishi Sunak confronted Li Qiang, China’s premier, over the “unacceptable” interference in British democracy.

The Telegraph understands that security services suspect a number of Chinese agents to be working in Westminster, and are planning to use the National Security Act, passed this summer, to detain them.

The Act introduced an offence of “foreign interference”, making it illegal for spies to meddle in elections or disrupt the workings of parliamentary democracy in the UK. Working covertly for a foreign hostile power will now become a criminal offence.

The two men were arrested on suspicion of offences under the old Official Secrets Act, which dates back to 1911 and is much harder to prove, because their alleged offences occurred before the national security act came into force.

House of Commons authorities are now facing questions over how the researcher was able to obtain a parliamentary pass, with Luke de Pulford, the director of the Inter-Parliamentary Alliance on China, calling it a “massive due diligence failure”.

Sir Lindsay Hoyle, the Commons speaker, is widely expected to address MPs on Monday amid calls for a review of the vetting process.