Millions of Britons are failing to declare their weight loss injections to insurers, which in turn could land them with huge bills if they fall ill abroad.

Drugs such as Mounjaro and Wegovy have soared in popularity since their approval by the NHS to help tackle diabetes and obesity, while demand for private prescriptions is also rising.

Now those using the jabs are being warned that if they plan to go on holiday, they're at risk of invalidating all-important travel cover.

Data from travel insurance provider Staysure shows the use of weight loss drugs has been declared in just 0.06 per cent of travel insurance quotes over the past two and a half years, a fraction of the 2.4million people estimated to have access to them.

Even allowing for differences between the wider population and those who buy insurance, Staysure says there is a 'clear gap' between the use of the jabs and the proportion of those who declare them to their insurer.

The monthly declaration reached 0.227 per cent in June, lower than the estimated 1.7 per cent usage rate.

Any traveller who takes out insurance must declare pre-existing conditions and medication. 

However, it is likely that many who are on weight-loss jabs may not consider it as medication or forget to declare it when buying cover.

This is Money previously warned that failing to declare weight-loss jab usage and any associated health conditions may mean your insurer refuses to pay out if you make a claim.

That could see travellers exposed to claims that risk ballooning, with Staysure highlighting one claim that was initially estimated at just over £20,600 which rocketed to more than £147,500 as treatments progressed.

Of the customers who declare weight-loss injections, around 98 per cent also have multiple medical conditions recorded on their quote, which mean they are at greater risk.

Staysure claims data reveals between January and May, medical treatment and repatriation claims from the US surpassed £371,000, while India topped £263,000 – including one claim of £128,336.

In Spain, one of the most popular short-haul holiday destinations among Britons, total claims exceeded £314,000, with one medical emergency costing £88,448.

Simon McCulloch, chief commercial officer at Staysure, said: 'The safest approach is to answer every medical screening question fully and accurately when you buy a policy, then tell your insurer if your health or medication changes before you travel. 

'A quick check with your insurer before departure can prevent uncertainty when you are abroad and need help.

'Declaring a condition or prescribed medication does not automatically mean the price will rise. 

'It gives the insurer the information needed to assess the risk properly and confirm what is covered, which is far better than discovering during a medical emergency that important information was missing.'