Ensuring travellers have overseas medical insurance when they confirm a holiday option is "an essential part of the booking process", according to Trailfinders.
Lucy Balding, spokeswoman for the organisation, said: "We strongly advise all of our clients to take out travel insurance when they pay the deposit on their holiday."
Her remarks come after the British Foreign and Commonwealth Office (FCO) released a survey indicating that almost a third (31 per cent) of respondents have not taken out overseas health insurance for their past winter sports holidays, while 61 per cent said they were unaware that many travel insurance policies do not cover off-piste accidents.
Just 16 per cent of people said they always read the small print of their international health insurance policies.
Meanwhile, separate research from Sainsbury's Finance revealed that the average cost of hospital treatment overseas currently stands at £2,040, an increase of 6.25 per cent year-on-year.
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