The country's special tax investigation unit is looking into the account of the company running the track and payments to the promotion company of the Belgian Grand Prix.

The firm is run by Slavica Malic, the Croatian wife of F1 supremo Bernie Ecclestone.

According to Joseph Moxhet, chairman of the company running the circuit, investigators are looking for the equivalent of £125,000 in due taxes and fines for 1993 alone.

Some media reports put the figure much higher.

It follows a row over tobacco advertising at the track in southern Belgium.

Calendar due this week

"It sure comes at a bad moment," said Andre Maes, secretary general of the Spa-Francorchamps circuit.

The sport's governing body, the FIA is due to rule on next year's calendar on Thursday or Friday.

The Belgian GP is penciled in on the provisional schedule but Maes realizes this could change quickly.

"We have had no contact with FIA about this. This goes over our head," he said.

The Belgian Grand Prix is one of the most attractive weekends of the Formula One circuit, with the race using public roads for much of the 4.3 mile distance.

Drivers consider the sweeping curves and the undulating track that cuts through the dense Ardennes forest, the best in the world.

Last year's race was also the most dramatic of the season, featuring several crashes in torrential conditions, including a massive pile-up at the start and a controversial accident between Michael Schumacher and David Coulthard.

Tobacco threat

Maes already has been at the forefront of a battle to keep tobacco advertising on his circuit despite the prospect of a stringent Belgian ban, due to come into operation on 1 January.

Cigarette adverts are an economic lifeline for Formula One and Ecclestone has threatened to pull races where tough anti-tobacco laws are in place.

On Wednesday, the area's regional parliament is due to vote on a local exception to the anti-tobacco law.

The Walloon government argues the strict national ban, which goes beyond European Union legislation, violates its regional autonomy rights.