British health officials are closely monitoring the swine influenza in Mexico and the United States because they are worried that the disease would become pandemic, according to the British Broadcasting Corporation (BBC).

The Health Protection Agency (HPA), the health watchdog in Britain, said in a statement that at present there have been no confirmed cases of human swine flu in the country or anywhere in Europe, and it is working with the government to review current incident and any threat it poses to the country's public health.

A British Airways cabin crew member was taken to hospital with flu-like symptoms on Saturday after falling ill on a flight from Mexico City to Heathrow. The spokesman of the hospital said the patient did not have swine flu.

So far 81 people in Mexico have died after contracting swine flue. But there have been no confirmed cases in Europe.

The HPA said there was currently a "very low level" of flu activity in Britain, but suggested that further investigation and vigilance over the severity and contagion speed of the disease should be needed.

However, some virologists warned that it was unclear how much drug resistance this new strain may have. People usually have no resistance to a new virus and there is nothing to stop it spreading from person to person and by various means around the world.

The British government has not advised people to avoid traveling to affected areas of Mexico and the United States. But the Foreign Office of Britain has recommended that anyone visiting those destinations or who has recently returned should consult a doctor when they have flu-like symptoms.

The World Health Organization (WHO) declared the outbreak in Mexico and the United States a "public health emergency of international concern" and urged all countries to keep a close watch for outbreaks of influenza-like illness.

Some affected in Mexico have tested positive for a strain, H1N1, and 11 people in the United States had been infected by the virus, according to the WHO.

Swine flu is a respiratory disease that infects pigs and does not normally infect humans. But sporadic cases do occur, usually for people who have had close contact with pigs.