Notwithstanding the favourable exchange rate for British holidaymakers heading to the US, medical expenses in the states remain sky high and travel insurance is vital.

This is according to the financial services giant American Express, which is advising travellers to invest in suitable cover before facing the reality of a hefty fee on the other side of the Atlantic.

Last week, the pound reached a 26-year high against the dollar, making American goods cheaper for British visitors.

But despite the appeal of low-cost transatlantic flights, holidaymakers should not underestimate the expense of medical treatment in the US, warns Joanne Field, marketing manager at the New York-based card provider.

“The US is a very popular destination for Brits, especially when favourable exchange rates double our spending power,” she said.

“However, if you fall ill in the states, or need emergency medical treatment, it can cost a small fortune if you do not have the right travel insurance cover.”

Even tests in some clinics could run up bills that, without travel insurance, could be crippling, Ms Field added.