The BBC's Health Correspondent Richard Hannaford reports on the cost of a new anti-flu drug

The National Prescribing Centre has sent a bulletin to health service managers warning that the arrival of zanamivir or Relenza, which costs around £24 a dose, could "increase expectation dramatically".

Although doctors' organisations have already warned about the dangers posed by the drug, this is the first time the potential for chaos has been acknowledged by the NHS.

The document, obtained by Doctor newspaper, predicts that 4.8 million people could need the drug during an epidemic year.

Until now, there have been no prescription drugs which help ease the suffering of flu patients - but this does not stop them approaching GPs for help.

Ad campaign ineffective

During the last epidemic, in the winter of 1989/90, 600 people in every 100,000 went to see their doctor with flu, even though a massive advertising campaign told them not to bother.

The fear is that with the first ever treatment for flu available, many more people will demand it.

The NPC says that consultation rates of just 400 in every 100,000 people mean that GPs have to suspend nearly all their other routine work.

Practices, it adds, would "go into crisis mode".

"In the current format of primary care, it is difficult to see how it might cope with such demand at times of epidemic."

The NPC's role is to provide and help co-ordinate the provision of effective information on medicines and prescribing related issues mainly to Health Authorities and GPs.

The drug's makers, Glaxo Wellcome, said that the NPC estimates were over the top. It does not expect more than 500,000 people to receive the drug in an average year.

Relenza, now licenced for use in the UK, has been shown to cut the length of flu attacks by up to two days if taken promptly.

The drug has been referred by the government to the National Institute for Clinical Excellence, who will decide whether it is sufficiently effective to allow it to be freely available on the NHS. A decision is expected by November.