It is better known for its ancient temples, beautiful beaches and mouth-watering cuisine, but Thailand is also the deadliest destination for British holidaymakers.

As millions prepare to flee a British summer that has been at best lukewarm, the Foreign and Commonwealth Office published figures yesterday showing the countries where Britons are most likely to seek help from their embassy.

Unsurprisingly, Spain, which attracts about 14 million Britons a year, tops almost every category for holidaymakers in peril. But when the figures are adjusted to show the proportion of travellers affected, Thailand is by far the most dangerous.

Australia and India, also favourite backpacking destinations, are ranked second and third for the ratio of British visitors seeking “serious assistance” - where more than advice is needed. Britons are also most likely to lose their passport Down Under.

Perhaps surprisingly, Britons are arrested at a higher rate in the United States than in any of the other ten countries where they most need a British embassy for help.

The Foreign Office said that the Thailand figures, for April 2005 to March last year and released in British Behaviour Abroad, showed that “although Brits are getting more adventurous, they are not doing enough preparation before they go”.

The 381,000 who travelled from Britain to the SouthEast Asian kingdom were nearly five times more likely to die than those visiting the second deadliest - India. They were also 50 per cent more likely to be taken to hospital in Thailand than in second-placed Greece. About 24 out of 10,000 Britons needed serious assistance from a consulate in Thailand, double the rate of those visiting Australia.

Travel agents said that the problems arose from cheap flights and underprepared travellers. A spokesman for the Association of British Travel Agents said: “The majority of people travelling to Thailand are back-packers. They often travel uninsured and stay in cheap accommodation. If you’re travelling like that for an extended period you are more likely to end up with a problem.”

One staff member of the British Embassy in Bangkok, who wished to remain anonymous, said: “The embassy is having to devote more and more resources to these kind of problems. But we can’t send away British citizens who need help.”

The Czech Republic has become a surprise addition to the destinations where Britons most often encounter problems. The report says that it features “as one of the countries where most consular assistance is required, with a disproportionate number of lost passports, arrests and hospitalisations. This is likely to be due to the massive influx of hen and stag parties to Prague.”

Britons in search of cheap alcohol are the second-biggest group of visitors after Germans, said David Frous, of the Czech Embassy in London. “I cannot deny that the number of potential problems relating to stag parties is large,” he said. “But there are large numbers of UK nationals coming to the Czech Republic, so as well as more good people, you get bad people too.”

But British diplomats said that most of their work involved dealing with Britons who fell prey to petty crime. Peter Wickenden, second secretary at the British Embassy in Prague, said: “A relatively small proportion of our consular assistance is taken up with Britons causing trouble.”

Diplomats have been visiting brothels in the city, distributing Foreign Office-branded beermats and posters warning British visitors against “sobering up in a cell”.

Meg Munn, Foreign & Commonwealth Office Minister, said: “One of the most important tasks for the Foreign Office is our work to help British nationals in distress overseas. As this report shows, although some of the incidents people face are unavoidable, many can be prevented with a little planning and careful preparation. Simple precautions – like researching your destination, getting comprehensive travel insurance, checking medical requirements and taking copies of important documents – could help in the long run to avoid common traumas, risks and dangers.”