Two-thirds of British adults plan to go abroad in 2017 and more book holidays at this time of year than any other, but many leave themselves open to financial disaster by failing to arrange travel cover at the same time.

While January and February are peak months for last-minute winter sun and snow sports breaks, travel industry association ABTA said a third of all summer holidays are also purchased at this time of year.

According to Sainsbury’s Bank, around 34 million people aim to travel overseas this year, but almost 40 per cent will not take out insurance when they should.

Thirteen per cent will buy it with more than a week to go until departure, six per cent will wait until the last week, and a further one per cent will do it the day they leave. A further 18 per cent - almost one in five – will not take cover at all.

Alan Sanderson, head of insurance at Sainsbury’s Bank, said: “Whilst lots of holidaymakers are early bookers who like to plan ahead so they have something to look forward to, our research shows that many don’t pay the same attention when it comes to travel insurance.”

The bank calculated that holidaymakers forced to change their plans due to an unexpected illness or incident would face an average cancellation cost of £816 per person.

Many people assume insurance is not necessary if they have a European Health Insurance Card (EHIC), but this provides only limited medical benefits within a defined area and gives no protection for occurrences such as cancellation, delay or baggage loss.

The EHIC covers European Economic Area countries, including all 27 members of the EU, Switzerland, Iceland, Norway and Liechtenstein, but it is not accepted elsewhere.

Within these countries, it entitles the bearer to the same level of state medical care provided to eligible nationals. However, state care varies dramatically and few countries cover the full price of treatment.

For example, in France patients may have to pay for a consultation with a doctor with up to 70 per cent of the bill reimbursed later. They may also have to contribute towards the cost of staying in hospital overnight.

The EHIC provides no cover for mountain rescue or medical repatriation and there is no guarantee of being taken to a state facility, as many hospitals and clinics in ski resorts are private, where the EHIC may not be accepted at all.

This means that failing to complement it with appropriate insurance can be extremely costly. In 2015, UK insurance association the ABI paid out £1 million a day to travel policyholders who had been billed for medical costs. The average claim was £1,200 but some accidents – particularly those involving winter sports – cost a lot more.

According to the ABI, a skier who suffered serious bruising when he was hit by a snowboard in France was charged £5,425 after being evacuated from the mountain by helicopter.

Another skier airlifted to a French resort clinic and later transferred to a bigger hospital after a spinal injury was charged £8,978 for transport, while a woman who tore her anterior and interior cruciate ligaments skiing in Austria had to pay £9,439 for surgery to repair them.

Meanwhile, insurer Aviva put the average cost of treating spinal cord injury abroad at upwards of £31,000, knee damage at £24,000, a dislocated ankle at £22,000 and a leg fracture at £16,000.

Alex Edwards, travel insurance spokesperson at Gocompare.com, said: “Skiers and snowboarders, and even those who are just going along for the trip, should always arrange suitable travel insurance to ensure they’re protected for medical treatment and medical repatriation if necessary.

“Other advantages of having proper winter sports cover include protection against losing your skis, your lift pass and other equipment, and some even offer compensation if there’s no snow in your resort.”

Do not simply take the policy offered by your travel agent or bank, though, as you could end up overpaying. Single trip cover for two skiers is available from as little as £13 if you shop around on price comparison sites.

But read the small print and ensure you are getting sufficient protection. MoneySuperMarket recommends having at least £2m of medical cover (£3-4m if going to the US) to pay for mountain rescue, prolonged treatment or repatriation by air.

It also advises having £1m of personal liability protection to cover against being sued after an accident, cancellation cover for the total cost of each person’s holiday plus pre-paid activities and excursions, enough baggage cover to replace everything being taking, and at least £250 for the theft of cash.

Compensation for scheduled airline and end-supplier failure is also desirable, as is payment for delays. And, to ensure claiming does not become too expensive, holidaymakers should aim for an excess of £100 or less.

Most single-trip policies do not include winter sports as standard so anyone planning to ski or snowboard will need to add this or buy a dedicated winter sports policy.