by Jennifer Clarke BBC Radio 4's Money Box

Only last week the Foreign Office warned that taking advantage of low cost flights without travel insurance was risking financial ruin.

Around 40% of British travellers often fail to take out proper cover for short breaks overseas.

But even those of us who think we are covered may not be.

Heart attack

Theresa and Mike Roynon have been Nat West customers for 30 years.

In 1999 they were invited to "upgrade" their account to the bank's Advantage Gold service.

Nat West offers travel insurance on a number of accounts

For �6 a month they got a number of benefits including free travel insurance.

The couple have relied on it ever since.

When Mike had a heart attack in Greece last month, they rushed to a local private hospital, confident that their insurance policy would cover the cost.

Theresa contacted the insurance company and was given a reference number for her claim.

Mike was admitted and doctors started investigating his case.

But the Insurance company called back and told Theresa the couple were not covered as she had paid for the holiday with her Advantage Gold Switch card instead of her Advantage Gold credit card.

Cockroaches

Theresa was horrified. "I could not take it in. I just felt numb and sick.

"They just left us alone in a foreign country without any help. I mean you would think you would have your passport, not nearly lost your husband"

Theresa had to take Mike to a public hospital where the conditions were tough.

There were cockroaches in the wards and Theresa had to make a 4 hour round trip every day to bring Mike clean bedding and fresh food.

The couple had to stay in Greece for an extra 11 days, before they got the all clear to bring Mike home on a normal flight.

Medical bill

By the time they got back to the UK, the medical bill, the flights home and the extra accommodation costs had risen to more than �2,000 - money they simply did not have.

Nat West... did not state to me that I should pay by a Mastercard

Theresa Roynon

Theresa told Money Box "I had no way of paying it.

"I have got to go to Citizens Advice so they can get in touch with people in Greece to make arrangements for me to pay it monthly because I have not got it".

The couple are adamant they had no idea that paying for the holiday with her debit card rather than her credit card would invalidate the insurance.

Previous trips

Theresa was horrified when she realised she had not been covered on any of their previous holidays either, including trips to Crete and Tenerife with their four year old grand-daughter.

"Nat West told me the minute I stepped out the country I was covered.

They did not state to me that I should pay by a Mastercard. If they did I would have.

I would not take my grand-daughter out of Bristol without insurance."

Terms and conditions

Nat West told Money Box it believes its terms and conditions are very clear.

In order to get the insurance you must pay for all of the holiday using an Advantage Gold credit card.

Payments made with the Advantage Gold debit card do not count.

Honest mistake

After insisting there was nothing it could do for the couple, on Friday Nat West told Money Box it had reconsidered.

In a statement the bank said: "Having reviewed this case, we feel that the Roynons made an honest mistake and in light of the upsetting circumstances they have faced, we are prepared on this occasion, as a gesture of goodwill, to deal with the claim as if all of the travel had been paid for on the credit card."

But the bank maintained the rules were both fair and clear.

It urged its 1m Advantage Gold customers to "familiarise themselves with the terms and conditions" before using the policy.