The government's chief medical officer has warned that Britain will inevitably be hit by cases of swine flu at some point.
Sir Liam Donaldson was speaking after a meeting of British health experts to discuss how to stop a deadly outbreak of swine flu from entering the country.
The human strain of the virus, usually associated with pigs, has killed more than 80 people in Mexico, while cases were reported in the US, Spain and New Zealand.
A Canadian woman is being treated for suspected swine flu at an undisclosed hospital in Manchester, and two people who returned to Scotland suffering "flu-like symptoms" after returning from Mexico are being assessed in hospital.
Meanwhile, Health Secretary Alan Johnson confirmed that a man taken to a London hospital after arriving at Heathrow on a flight from Mexico City did not have the H1N1 strain of the virus.
He promised BBC1's The Politics Show that travellers coming into the UK with flu-like symptoms would be examined "very, very quickly" by the NHS.
No cases of swine flu have yet been confirmed in Britain.
The NHS has a stockpile of more than £500m worth of the Tamiflu antiviral drug, which has proved effective on patients in Mexico, and scientists are working on developing a vaccine against the new strain, said Mr Johnson.