British travellers are dangerously ignorant about potentially fatal tropical diseases, new research showed today, with three million Britons in the last five years not bothering to take recommended preventative measures before visiting high-risk areas.

Some 21% of those questioned in a YouGov survey said they had not vaccinate themselves or their children ahead of a holiday in a tropical destination.

Despite a growing taste for holidays in Asia, South America and Africa, around one in 10 travelling Britons have left themselves unprotected in the past five years against malaria, which annually kills over a million people worldwide.

Some 25% of those who did not take anti-malarials said they assumed they were not at risk from the mosquito-borne infection.

UK deaths from malaria doubled from 2002 to 2003, and doctors raised concern at today's findings, adding that British travellers needed to be more aware of the symptoms of the disease as well as the risks.

Dr Peter Mace, assistant medical director for BUPA Wellness, said: "People see malaria relatively rarely so they're not as quick to be diagnosed as they might be. This may allow the disease to progress further.

"Generally malaria prophylactics have little side effects for most people, so there's no reason not to take them."

Malaria could also lead to kidney damage or heart problems, he warned.

YouGov surveyed 2,200 people for Direct Line Travel Insurance.

· Travellers planning to visit tropical areas are advised to seek medical advice at travel clinics or GPs' surgeries six to eight weeks before they intend to travel