London - Three people are currently undergoing specialist tests for suspected swine flu in Britain after their recent return from Mexico, Health Secretary Alan Johnson said Monday. He told parliament that the three patients were kept in isolation wards in hospitals in Scotland and in the northern city of Manchester after developing "flu-like" symptoms.

A further 14 people were undergoing "initial investigation" but were not treated in hospitals.

A total of 25 suspected cases of the disease had been reported in Britain, of which eight had proved negative.

No case of an infection with the virus has so far been confirmed in Britain.

Johnson described the outbreak as a "significant health threat" but underlined that it was "too early" to say whether it would develop into a pandemic.

If the virus started spreading widely in Britain the government was "well-prepared" with a stockpile of anti-viral drugs to treat 33 million people - or half the population.

Entry checks on passengers arriving at ports and airports had been "enhanced" as a precaution, while no travel restrictions to the affected areas had so far been imposed by Britain, said Johnson. (dpa)