It boasts the “world’s most extravagant cocktail” at £5,000 a pop and has become the Alpine playground of royalty and celebrities since opening two months ago. But the British-owned Club Coco in the Swiss resort of Verbier is facing damaging legal claims over a humble shot of tequila.

Seven British holidaymakers are seeking compensation from the club after being given caustic soda instead of salt to accompany their après-ski drinks.

The waiter is believed to have mistaken the chemical for salt after it was left on the bar by cleaning staff.

A police investigation into the incident in the early hours of February 13 led to the club being closed for a week after officers raised concerns over health and safety issues.

The skiers, from Hertfordshire, felt burning in their mouths and on their lips after drinking their tequilas, Swiss police said. The men were taken to a doctor and later to a specialist in a clinic where some were kept overnight and treated for lesions.

The ski group reported the incident to the police, who inspected the club and took a sample of the caustic soda to a forensic laboratory, where experts confirmed that the victims’ injuries and skin irritations were caused by the cleaning product.

The seven victims are taking legal action against the club and have filed a complaint against the owners. Prosecutors conducted an inspection and ordered the club to be closed after establishing that hygiene regulations were violated on several accounts. The club was closed on February 27 and allowed to reopen on Wednesday.

A spokesman for the Valais cantonal police told The Times: “We have conducted a thorough inspection of the club. It was determined that the waiter had mistakenly used the caustic soda as it was left right next to a box of salt.

“But we also found other irregularities: the ice was not up to hygiene standards, and the food — the fruits in particular — were not sufficiently fresh. The club was badly run in terms of health and safety regulations so we decided to close it down.”

The man behind Club Coco is Harvey Sinclair, a London-based entrepreneur who made more than £3.5 million in the sale for £55 million of his online recruitment company Hot Group to Trinity Mirror in 2005. He founded the club with a number of Geneva-based oil traders.

After a £1 million refurbishment the club reopened shortly before Christmas with the models Jodie Kidd and Astrid Muñoz and the comedian Patrick Kielty flown to Switzerland for the opening party.

The members-only club is seen as one of most glamorous in the Alps. The singers James Blunt, Diana Ross and Phil Collins have homes in the resort and regular visitors include the Duke and Duchess of York with their two daughters.

The wallpaper at Coco is handpainted, the curtains are fur and one wall is covered with £30,000of gold leaf.

A spokesman for the Coco Club said: “It was an unfortunate incident due to human error. The person responsible for the incident has been dismissed. Measures have been put in place to ensure this never happens again.”

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