Britain is braced for a pandemic of birdflu which could result in at least 50,000 deaths throughout the country, the government's chief medical officer Liam Donaldson said on Sunday. His comments followed laboratory test results on Saturday which showed the same deadly H5N1 strain of bird flu as that found in Turkey and Asia had infected ducks in Romania, confirming the virus had reached mainland Europe. Donaldson said history suggested the bird flu virus could combine with a human flu virus and become easily transmissible. "Once in a while, every 10 to 40 years, the flu virus mutates into a strain which we haven't got natural immunity to," he told BBC TV. He said a normal winter flu kills more than 12,000 people in Britain. "If we had a (birdflu) pandemic the problem would be the existing vaccines don't work, we would need a new vaccine and people don't have natural immunity," said Donaldson. "So the estimate we are working towards is around 50,000 excess deaths from flu, but it could be a lot higher than that -- it depends on whether the strain is mild or serious." He said Britain was preparing for a pandemic by stockpiling anti-viral drugs which can reduce the severity of attacks and prevent some deaths. He said restricting peoples' movement would not be a priority.