Nearly 1.3 million Brits with pre-existing medical conditions travelled abroad without telling their travel insurers about their health issues.

A move that is jeopardising insurance cover as well as holiday-goers' finances.

Sam Marrs, Sainsbury’s travel insurance manager, said: “Withholding key information such as any medical conditions could, however, mean your cover may be invalidated and in the worst of cases, this could mean facing large hospital bills or arranging your own repatriation.”

Over the past 12 months, Sainsbury Insurance estimates that 267,000 people with heart problems travelled and did not tell their travel insurance companies about their condition. A further 206,000 people with respiratory conditions and 149,000 cancer sufferers survivors did the same.

An additional 500,000 people with medical conditions went abroad over the past year with no travel insurance.

Mr Marrs said: “It's important to be honest with your insurer and provide all the information they ask for.

“It's simply not worth taking the risk and travelling with potentially invalid cover or no cover at all.”

Cost and fear of refusal were two of the main reasons why people did not tell their travel insurers about their medical conditions. Fifteen per cent said they feared they would be refused cover.

A further 19 per cent said the omitted information because they believed they would secure a cheaper premium.

When informed of medical conditions, most insurers will apply a slightly higher premium, but they will provide cover for most medical conditions.

Mr Marrs said: “It's a fiercely competitive market so if you have a common medical condition there's a good chance you'll find an insurer to cover you for a fair and competitive premium.

"The purpose of travel insurance is to ensure that if a disaster does strike, you'll receive the necessary care and support.”