The controversial link is designed to close the Antwerp Ring on the eastern side and ease traffic from the left bank of the Scheldt to the motorways heading for Germany, France and the Netherlands. But the latest announcement means that the Flemish government is obliged to begin the whole planning procedure over again, which would result in a delay of at least three years.

Opposition to the plan is focused on a long bridge/viaduct which would take traffic, including heavy trucks, through a part of the centre of Antwerp which includes homes and schools. As well as a noise nuisance, the traffic would increase the levels of pollution by diesel particulates in the air, critics say. Opponents also argue that the Lange Wapper would do little to ease congestion.

The case was brought by restaurateur Gunther Dieltjens, who with his wife and a staff of 50 runs the Pomphuis restaurant, installed in an imposing pumping house dating from 1920. The Lange Wapper would pass directly over the restaurant and pillars bearing the weight of the viaduct would need to be constructed in his car park and next to the terrace.

"I'm happy I did this for the city," Dieltjens said after the auditor's advice was given. "Obviously I also did it for my business, but I wasn't only driven by commercial interests. The city is better off without that bridge." Protest group StRaten Generaal said the advice was "important and hopeful, not only for this but for other planning cases."

The Antwerp Mobility Management Agency (BAM), which is responsible for the project, has not yet responded to the auditor's opinion.

• Ademloos, one of the groups protesting at the Lange Wapper plans, last week handed over a petition of more than 66,000 names to Antwerp mayor Patrick Janssens. "This is a historic and joyful day," said Ademloos chairman Wim Van Hees. The petition has raised more than enough signatures to force the issue to a referendum involving the people of Antwerp.