Nicholas Mockford, 60, an executive for ExxonMobil, was gunned down as he left an Italian restaurant in a suburb of Brussels.

He was shot three times, once as he lay on he ground, and his Belgian wife was left beaten and covered in blood, cradling her husband who died on the way to hospital.

Yesterday, an Exxon Mobil spokeswoman said: "We were shocked by the tragic death of Nick Mockford, one of our employees, in Brussels. Mr Mockford was a department manager at our office close to Brussels, but we have no indication the incident was work-related."

Witnesses say they saw Mr Mockford and his wife walk across the street to their Lexus car before shots rang out.

Two men were then spotted running away from the scene, one holding a motorcycle helmet.

The shooting happened on October 14 but news of the attack has emerged only now because Belgian police had imposed a blackout.