Health officials are to monitor the presence of foreign insects amid increased fears that lethal tropical diseases could hit Britain.

The Health Protection Agency (HPA) said Asian tiger mosquitoes, which can carry potentially lethal diseases such as dengue fever, have been found recently in UK ports.

Experts suspect that global warming and climate change could help the insects to survive in Britain and increase the risk of deadly diseases.

Although there is no suggestion that anyone has been infected so far, the HPA said it would step up measures to prevent tropical mosquitoes and other insects arriving in the UK.

Asian tiger mosquitoes have been found in container ships docking at British ports, and have also entered other countries, such as the United States.

Scientists have warned that by 2050 global warming could lead to outbreaks of malaria in some parts of Britain. Agency officials will examine how climate change could impact on insects and the spread of diseases.

Dr Pat Troop, the HPA's chief executive, issued the warning as she set out the agency's first five-year plan of action yesterday.

Sir William Stewart, chairman of the agency, said the ease of modern travel "had a lot to answer for" in increasing the risk of tropical diseases. "The Sars experience demonstrated that a new bug can spread around the world in days," he said. "Compare that with the months and years it took the Black Death to spread via sailors and traders. Faster travel means faster transmission of bugs."

The HPA, which was set up in April, will be responsible for drawing up Britain's plans for dealing with biological and chemical attacks, as well as coping with diseases such as Sars.