Swiss police on Wednesday said they were investigating 12 cases in which British tourists ignored quarantine orders designed to stop the spread of the new coronavirus variant.
Hundreds of British citizens are believed to have fled the country.
On December 21, the Swiss government placed people who arrived from Britain and South Africa since December 14 under a 10-day quarantine. They were supposed to stay indoors, away from other people.
Flights were temporarily halted, meaning some were stranded in resorts including Verbier, a popular destination for British skiers.
The canton of Valais, which includes Verbier, sent 220 police to enforce restrictions, including operations in which they checked up on selected tourists.
"Of the 150 people who were checked in at the holiday destinations, 138 guests consistently adhered to the quarantine," Valais police said.
"Investigations are under way in 12 cases where the tourists had already left the canton."
But far more than a dozen left. Hundreds of Britons fled quarantine in Verbier.
At least seven people in Switzerland were found to have the mutated virus, five with the British version and two with the one detected in South Africa.
The penalties that the British tourists, some of whom own Swiss holiday homes, could face in Valais is unclear.
Laws governing "dangerous diseases" could mean quarantine breachers are fined up to 10,000 Swiss francs ($11,343).
Switzerland is sticking to a light lockdown, shutting restaurants but leaving ski areas open as it balances health considerations with the economy.