If you are willing to fly to Berkshire from the South of France for bacon-and-egg ice cream, a little health scare is not going to put you off.

Heston Blumenthal’s restaurant, The Fat Duck, opened for the first time yesterday in two and a half weeks after 400 diners reported becoming unwell with an unexplained illness. It was fully booked for the lunch service.

The Health Protection Agency insisted that the restaurant had not yet received the all-clear. Tests are continuing, but so far it has found nothing wrong, and has allowed the restaurant to reopen.

The first diners to arrive seemed unfazed by the problems. “We understand that the swabs have been negative,” Nichola Barnett said. “I can’t believe a place like this would have bad hygiene. I’m looking forward to the experience.”

Ms Barnett, 43, is a chef on a motor yacht in Antibes. On a brief trip back to England, she took her boyfriend as a late birthday treat.

The health scare turned out to be the only way that she could get a booking. “We wanted to come anyway, but we tried to book after it shut, and we only made it on Monday.”

A full complement of 40 chefs, plus 15 front-of-house staff, were on hand to look after the 40 diners.

Bryan Lynch attended a 40th birthday surprise lunch as a gift from his partner. “I only knew I was coming here this morning,” he said.

Did the reopening come in time to save a birthday from being ruined? “Otherwise it would have been Le Gavroche,” he said. “But I’ve wanted to come here for a long time.”

Blumenthal said: “It’s fantastic. The staff and everyone are ready to go, buoyant and energetic.” The chef described the past two weeks as his “worst nightmare” with kitchens shut down while health inspectors crawled all over them.

Shellfish has been withdrawn from the menu — purely as a precaution — Blumenthal said.

It meant that his Sound of the Sea, a concoction involving clams, oysters and edible sand, had to be modified. The accompanying iPod, which gives diners a suitably maritime soundtrack to the dish, remained unaffected.

Blumenthal said that the closure had been “very, very costly” and could end up losing him £300,000.

He said that he had had calls of encouragement from chefs all over the world. Ferran Adrià, of El Bulli, in northeastern Spain, had been especially supportive. The diners also seemed pleased with the results.

George Flo, 29, a company director, was cautious. “I’m just expecting it to be a bit more clinical — there’ll be a lot of scrutiny today,” he said before his meal. But four hours later, he left happy, describing the experience as “mindblowing”.

Gail Gallie, from North London, had been celebrating her 38th birthday. “Really fantastic,” was her verdict. “The best birthday treat I’ve ever had. We’ve been wanting to come for three years. It was worth the wait.”

Her friend Jim Godfrey was equally impressed. “Heston was very relaxed,” he said. “He knows what he’s doing.”

Even the taxi driver waiting to pick up guests did not have a bad word to say. “I’ve been doing this for five years and I’ve never had a complaint. They all love it.”

Patricia Thacker was celebrating her 64th birthday. “There was magic with every dish,” she said. “Everything is so different.”

Her husband was the first person of the day not to offer up a single superlative. “It was fine,” he said. “But I’m not really into that sort of thing.”

Explore Food & Drink

• Gordon Ramsay

• Heston Blumenthal

• Recipes

• Wine

• Real Food

• Drinks

• Anjum Anand

• Eating Out

• Video Recipes

Times Recommends

• Top Ten most searched for recipes
• Chalet Chef 2010: the winning menus
• Gin and pomegranate jellies