A former british spy is under investigation by uk and belgian intelligence agencies over a suspected influence-buying operation by china, in the latest sign of european fears about beijings sway on the continent.

Fraser cameron, who now runs the eu-asia centre think-tank in brussels, is alleged to have been involved in selling sensitive information to chinese spies actions that posed a clear threat towards the european institutions based in the belgian capital, the countrys state security service said.

Mr cameron had been a member of the uks secret intelligence service, known as mi6, until the early 1990s, according to a person familiar with the investigation. he then worked for the european commission, where he specialised in foreign policy and had a spell in washington. he retired from the commission in 2006 to pursue a career in think-tanks and consultancy work.

Mr cameron has denied any wrongdoing and has branded the allegations bizarre.

The investigation into his alleged links with chinese intelligence officials was run jointly by mi5, the uks domestic spy agency, and the belgian state security service. mi5 has now issued an espionage alert to warn overseas intelligence agencies and governments that mr cameron poses a potential security risk.

Although he is not accused of leaking classified information, one person familiar with the investigation said it had raised concerns that the ex-spy had a willing relationship with members of the chinese intelligence services.

Belgiums state security service said the case should be a clear signal that anyone who is involved in espionage in brussels will sooner or later be on the radar of the intelligence services and will not be able to continue his activities with impunity.

Mr cameron is alleged to have been paid for information by two accredited chinese journalists in brussels who were also intelligence agents, according to people familiar with the probe first reported in belgian media and politico. the belgian-british investigation has been going on for several years, but it may be that the alleged behaviour even if proved would not constitute a crime under either countrys laws.

The case comes as some european countries, under us pressure, are toughening their security policies towards china through actions such as curbing huaweis involvement in next-generation 5g mobile telecoms networks.

Brussels has become a particular focus for european concerns about chinese influence because it hosts the headquarters of the eu and the nato military alliance.

Mr cameron told the ft the claims were ludicrous, utter nonsense and without any foundation. he denied he had been paid for information and said he had only learnt of the investigation when he started to receive questions about it from journalists this week.

This is a complete surprise, he said. i have had no access to any secrets or confidential information.

He added: there is a bit of a china paranoia thing going on at the moment.

The chinese eu mission and the european commission did not immediately respond to requests for comment.

The uk government has long been under pressure from intelligence agencies to toughen the official secrets act, and is expected to introduce an espionage bill to provide prosecutors with stronger powers against those passing information to hostile states. belgian security services are also keen to modernise espionage laws first written in the 1930s.

Andrew parker, who stepped down earlier this year as director-general of mi5, was quoted in a parliamentary report this summer telling mps that the official secrets act, some of which dates back to the first world war, had become dusty and largely ineffective and needed to be updated to reflect modern challenges such as combating influence operations.