Holiday makers who show symptoms of coronavirus while in the Isles of Scilly have been told they could face an “extremely pricey” visit.
The government says anyone who tests positive should return home as soon as possible to isolate for 14 days.
The islands are 28 miles off Cornwall, and the main ferry and plane providers are not accepting symptomatic passengers.
Options include paying for an extended stay or private transport.
A private jet boat to the mainland typically costs about £1000, with a week for a couple in self-catering accommodation in July or August costing about the same.
The islands have not had any confirmed cases. The tourist board for the islands said it was well prepared for an outbreak and could offer a “splendid visitor experience”.
A government spokesperson said the tourism sector could reopen as soon as 4 July and it “is finalising guidance”.
There are five inhabited islands and tourism represents 85% of the economy.
The St Martin’s Island Group, representing one of the islands, has posted advice on its website that it wants visitors to return, but warned: “If you begin showing symptoms of Covid-19 or are contacted by track and trace you can’t just jump in your car and drive home to isolate.”
It added it was “highly likely” the guest would have to cover the cost of the additional stay and “any travel or extra accommodation expenses of the incoming guests” booked to stay in the same facility.
“Your insurance is unlikely to cover this and so your holiday could become extremely pricey”, it said.
Other islands are also understood to be advising customers they will have to cover the cost of any extended stay relating to coronavirus.
If a guest is unable to return home they should discuss their circumstances with a health care professional and if necessary the local authority, the government said.