A previous British representative is under scrutiny for supposedly offering data to covert Chinese government agents, a Whitehall official says.
Fraser Cameron, who runs the EU-Asia Center research organization, is associated with passing delicate data about the EU to two government agents purportedly acting like Brussels-based writers.
He is claimed to have traded the data for a great many Euros.
In any case, Mr Cameron revealed to The Times the charges were "ludicrous".
The previous ambassador, who has worked for the Foreign Office and European Commission, says he has no admittance to any "mystery or secret data".
He disclosed to Politico that the claims "are without establishment", saying he has "a wide scope of Chinese contacts as a component of my obligations with the EU-Asia Center and some of them may have a twofold capacity".
A senior Whitehall official, who asked not to be named, told the BBC the examination had been a long-running joint request among British and Belgian insight and guaranteed that an advancement had come as of late.
He said this was an extraordinary case of how intently British knowledge functioned with its European accomplices.
The BBC's security reporter Frank Gardner says there have been developing feelings of trepidation about the degree of clandestine Chinese insight gathering in Europe, including over touchy arrangements between the EU and Britain over Brexit.
Belgium's state security administration is cited by the Financial Times as saying Mr Cameron's supposed activities represented "an unmistakable danger towards the European establishments" situated in the Belgian capital.
The examination is purportedly being controlled by Belgium's government investigators.