British holidaymakers without insurance who fall ill when abroad face medical bills of tens of thousands of pounds should the UK leave the EU without a deal, it has been warned.

Research by Admiral Travel Insurance found that one in four British travellers depart the country without relevant cover, putting them at risk of huge costs in the event of sickness or injury.

Britons are currently afforded free or reduced-cost treatment in EU countries by the European Health Insurance Card (EHIC). However, UK-registered EHICs will no longer be valid in the wake of a no-deal Brexit, leaving individuals to the foot the bill for medical services.

Admiral says, for example, the cost of treatment for food poisoning, usually covered free of charge by the EHIC scheme, will soar to as high as £2,000 in the likes of Spain, Greece and Portugal. The cost of having your appendix removed in France is £400 under the EHIC scheme, but will rise to £4,000 under a no-deal Brexit.

According to the Association of British Insurers (ABI), 3,000 people a week claim for emergency medical treatment abroad, with £200 million paid out a year.

Admiral has created a tool to show the cost of different treatments in different European countries for travellers without insurance. The prices range from £100 per X-ray and £150 for a doctor’s appointment to £4,800 for a broken leg and £32,000 for a heart bypass.

“It’s worrying that so many people are willing to travel to Europe without insurance and are relying on the EHIC in the event of a medical emergency,” said Cosmin Sarbu, head of travel at Admiral.

“Medical costs for different treatments already vary from expensive to extortionate between countries, and if the UK leaves without a deal, we could see those costs dramatically rise for British holidaymakers visiting Europe without insurance.”

Abta, the travel association, is advising holidaymakers to make sure they have “appropriate travel insurance, whether they have an EHIC card or not, as there are limitations to EHIC”.

It stated: “When travelling in the EU and beyond, it is important you take out travel insurance and check that it covers your current circumstances, including any medical conditions.

“If you have an annual policy, make sure you check the Terms and Conditions and contact your insurance provider if you’re not sure.”

According to the ABI, one medical bill in 2017 for treatment following a jet-ski accident in Turkey cost £125,000. Another for care following a stroke in the US led to a £760,000 bill.

The cost of the average medical claim in 2017 ran to £1,300, a 40 per cent rise since 2011.