This April 29, 2009, file photo shows stocks of antiviral treatment, Tamiflu, at a warehouse in an undisclosed location in the United Kingdom. For years, Britain has been preparing for the possibility of a flu pandemic. Now, with the arrival of swine flu confirmed here, the threat of a pandemic - a global outbreak of flu spreading rapidly because it is a new type of virus to which few, if any, people have resistance - appears a closer reality. The government's chief medical adviser Liam Donaldson said: " We have enough antivirals to treat half the population of the U.K. if they become ill." Associated Press