CBFA, which regulates the banking, finance and insurance industries, is empowered to act as an investigative magistrate in matters of insider trading and to hand out sanctions if appropriate. Bellens could face a fine anywhere between €2,500 and €2.5 million.

While CBFA itself declined to comment, the Bellens case appears to have been three years under investigation, despite the apparent simplicity of the circumstances. The regulator was also this week reported to be investigating a recent, more complex case of insider trading of KBC shares, dating from May this year.

The number of convictions by the CBFA is small, largely because the terms of the offence are not well defined, and the case is difficult to prove. The European Union is currently considering a "Market Abuse Directive", which would harmonise the terms of the offence in the EU, but member states are having trouble agreeing.