More info on the H5N1 mutation

‘The general departure from the progressive decline in 2004-2008 could mean that there will be a flare-up of H5N1 this fall and winter, with people unexpectedly finding the virus in their backyard,’ Lubroth said in a statement.

But leading microbiologist, Professor Hugh Pennington, says that while there is no evidence that the flu is yet mutating to spread from person to person it is a 'reasonable speculation' that it has become resistant to Tamiflu - the main drug used in the UK to fight the virus.

The British and Scottish Governments spent over £100m on over 50 million doses of Tamiflu - enough for 80 per cent of the population

The emeritus professor of bacteriology at Aberdeen University had warned last year that deadly flu pandemics with special antiviral drugs could create an even more dangerous, untreatable 'superflu' after the UK expanded anti-viral stocks from 35 million to 50 million.

The Scottish government's effort to combat a possible pandemic is also heavily reliant on Tamiflu, an oral drug produced by the Swiss manufacturer Roche, despite warnings that it may be ineffective.

"Tamiflu should only be given to high risk cases. I think it is a reasonable speculation to make - given the new reports - that Tamiflu has been handed out inappropriately and the virus has developed a resistance to it. If that is the case that would mean that the UK's stocks of the drug would be largely ineffective,' said Professor Pennington.

'The idea that Tamiflu was a cure-all was plainly wrong.

'There is no need to panic yet because there is no evidence that the virus is spreading person to person and there are other anti-virals - such as Relenza - that do have an effect.

'There is also no evidence that the virus is becoming vaccine resistant. A new vaccine will have to be made, but that is to be expected. Flu is always changing and it would be staggering if this flu didn't. Vaccines have to be constantly updated.'

However, the UK Government has stockpiled only about ten million doses of Relenza and it is more difficult to take. While Tamiflu can be swallowed as a pill at home, Relenza is a powder that must be administered with an inhaler, normally under medical supervision.

But Professor Pennington warned that stocks of Relenza had to be increased. 'We have to get as much Relenza as possible because we don't know how effective Tamiflu will be,' he said.

'With flu the best advice is to prepare for the worst and hope for the best.'

Prof. Pennington, a past president of the General Society for Microbiology, said it was also 'impossible' to predict when this year's flu would strike.

Dr Steve Gamblin, the joint head of molecular structure at the National Institute for Medical Research, has also previously warned that the mutation renders Tamiflu about 250 times less effective than it should be.

Sir William Stewart, the chairman of the Health Protection Agency, has also said that the widespread use of antiviral drugs to treat illnesses, including bird flu and seasonal influenza, is causing- viruses to mutate into drug-resistant-forms.

He has claimed that drug-resistant viruses now represented as big a threat to public health as antibiotic-resistant superbug bacteria, such as MRSA.

Concerns that a pandemic flu virus might develop resistance to Tamiflu first emerged in 2005, after reports from Vietnam that H5N1 virus was showing signs of decreased sensitivity to the drug.