Leading scientists say the UK government is failing to take advantage of scientific developments in the fight to prevent a flu pandemic.
The UK government is stockpiling millions of courses of Tamiflu
A Royal Society and Academy of Medical Sciences report says more than one anti-viral drug should be stockpiled.
It warns the H5N1 virus can develop resistance to Tamiflu, and says the drug Relenza should also be stockpiled.
Tamiflu's makers said there were only two instances of H5N1 patients showing resistance to the drug after treatment.
The report also calls for a special scientific advisor - to work alongside the Chief Medical Officer and the Chief Scientific Adviser - to advise ministers on planning for pandemic flu.
It also said the expert should work alongside the Chief Medical Officer and the Chief Scientific Adviser, to advise ministers.
And it calls on the government to work more with industry on vaccine production.
Sir John Skehel, chair of the report's working group, said: "We are concerned that decisions are being made, as the UK prepares for a possible pandemic, that fail to take account of expert advice.
"For example, the decision to continue to stockpile just one antiviral drug is a major concern. This needs to be reconsidered.
"New evidence that H5N1 can develop resistance to Tamiflu indicates that a combination of antivirals should be stockpiled by the UK for the most effective management of a pandemic."
He said the government was right to order Tamiflu in early 2005 - a stockpile of 14.6 million courses of anti-viral drugs is being built up
But Sir John added: "We are concerned that it is not updating its plans as the landscape of what we know about influenza changes."
Roche, the company which makes Tamiflu, said in a statement: "Resistant mutations of H5N1 virus have been detected in two patients at the end of treatment with Tamiflu."
By the end of the year, Roche would have the capacity to produce 400 million courses of Tamiflu per year, the statement added.
It would be up to the government and Department of Health (DoH) to determine strategies "along the lines of the principles established and outlined in the pandemic plan", it said.
The RSM said the government should consider increasing the size of the stockpile and should think about using the drug as a prophylaxis, a preventative treatment.
The report calls on the DoH to bring together academic researchers and pharmaceutical companies to develop vaccines which could be used to protect the public in the event of a pandemic.
It says it would not be possible to manufacture enough influenza vaccines globally in a pandemic - because experts will not know the make-up of a pandemic virus until it starts to spread meaning it would not be possible to immunise everyone.
However, the report adds that limited vaccine supplies can "go-further" if they are combined with adjuvants - agents which boost the effectiveness of a vaccine.
Sir John said: "We find limited evidence that the UK government is engaging with industry to research and develop new vaccines.
"Encouraging researchers and drug manufacturers to share information would speed up the development of adjuvants and vaccines to make the UK more responsive during a pandemic."
He added: "The UK is recognised as one of the most prepared countries in the world however research in this area must continue and up-to-date scientific information should be central to the government's decision making process.
"It will ensure we are prepared not only for a possible influenza pandemic, but also for any future emerging infectious diseases which may affect the UK."
But Professor Lindsey Davies, the Department of Health's Director of Pandemic Influenza Preparedness, said: "We are already addressing many of the report's recommendations in our ongoing pandemic preparedness planning.
"We will consider the recommendations of the report as we continue to develop this work."
She said the UK would continue to work with international partners, including the European Union and the WHO, on preparedness vaccine development.
Professor Davies added: "Our antiviral strategy is informed by international consensus and expert advice, and the current stockpile should be adequate to treat all those who fall ill in a pandemic of similar proportions to those in the 20th Century."
Shadow health secretary Andrew Lansley said further action was needed.
"If you believe, as I do, that there's a major risk of a pandemic flu on the scale of the 1918 pandemic of Spanish flu, we should think about stockpiling more antiviral drugs, stockpiling face-masks.
"And we should think about getting an H5N1 vaccine now, on the basis it will offer limited protection.
Liberal Democrat health spokesman Steve Webb said: "A national bird flu strategy must take into account the latest scientific advice on what will best tackle any pandemic.
"We cannot wait until after a case has been discovered to check if our contingency plans are the most effective to deal with this potential threat."