Health officials said today they were investigating 400 potential cases of food poisoning linked to Britain's top-rated Fat Duck restaurant, run by celebrity chef Heston Blumenthal.
The award-winning restaurant in Bray, Berkshire, is known for its chemistry-inspired dishes such as bacon and egg ice cream and snail porridge, with many courses frozen in liquid nitrogen.
Mr Blumenthal voluntarily closed the restaurant last month after around 40 diners complained of diarrhoea and vomiting.
The Health Protection Agency said the number had risen to 400 after media coverage of its investigation.
"This is a very complex outbreak," said Graham Bickler, a regional director at the agency.
The agency said its probe would extend to all those who had eaten at the restaurant since late January, whether they reported being ill or not.
The restaurant, which has had a three-star rating from the Michelin guide since 2004, is co-operating fully with the investigation, the agency said.
Diners often wait months for a reservation at the Fat Duck, which seats 40 people and charges 130 pounds ($185) a head for its 17-course tasting menu.
Mr Blumenthal has said he is mystified by the outbreak, as the restaurant conducts weekly infection tests and nothing has been discovered.
"It was out of the blue ... I'm as fastidious about the hygiene side of things as I am about the actual cooking processes," he told the Guardian website in a video interview.
"The last thing you want is somebody to leave the restaurant with so much as a slight headache."