The memo echoes warnings by a senior member of the House of Lords, who told The Times in May that the Government had been “caught on the hop” with the development of the service.

Lord Jenkin of Roding, who was asked to sit on the Lords’ Science and Technology Committee flu pandemic inquiry, described ministers as being “very slow” on the issue, adding that the flu line should have been critical to preparations over recent years, not just months.

Local NHS primary care trusts with well-established local plans were previously intending to have call centres and separate distribution centres where drugs would be available.

But the Government’s insistence on a national flu line with an uncertain start date means that trusts will instead have to take calls and distribute drugs from the same location.

It has been suggested that local pharmacies of community health centres could act as anti-viral collection points but the memo expresses doubt that these will be able to carry out symptom assessment and drug distribution. Staff at the collection points, who may not be medically trained, will require further training in swine flu symptom identification, anti-viral need and advice on doses.

When Dawn Primarolo, the Health Minister, appeared before the Lords committee last year, she said that the flu line would be ready by April or May, but the deadline passed and was revised as planners battled to get the system finalised.

The Department of Health said the service — which is designed to involve a call centre manned by 7,000 volunteers who identify swine flu symptoms, and allocate code numbers so that Tamiflu can be picked up from collection points around the country — would be ready by the autumn.

A contract to provide the flu line was agreed with BT only in December, but a health department spokesman insisted that since then all involved had been working “extremely hard” to have it ready.

When fully functioning, the system is designed to involve high-speed call management — a maximum of eight minutes per call — with suspect cases. People who call the line then nominate a “flu friend” to go to one of up to 500 collection points, take the medication back to the affected person’s home and post it through their door.

The current rate of patients reporting flu symptoms is as high as experienced last winter, when the NHS came under intense pressure at evenings and weekends.

Sir Liam yesterday announced his intention to develop an alert system, the NHS Pressure Rating, to assess demand if local hospitals, intensive care units and doctors’ surgeries appeared to be in danger of being overwhelmed.

“We want to come up with a index or a rating scale on the extent to which local NHS services are under pressure,” he said.

From containment to treatment: how the authorities responded

Containment People with swine flu have their diagnosis confirmed by lab reports. They, and anyone who has come into contact with them, are given the antiviral drug Tamiflu. Schools are closed to contain the spread of the infection. The Health Protection Agency (HPA) takes the lead.

Outbreak management Cases are diagnosed by a health professional without the need for laboratory confirmation, and the patient is given Tamiflu. Swabbing takes place on only a small sample of cases. People who have come into contact with a swine flu sufferer are unlikely to receive Tamiflu as a precaution. School closures are stopped in areas where community spread of the virus is sustained. Local health authorities take charge, with local HPA or NHS call centres used in areas of high infection.

Treatment GPs continue with infection diagnosis on the basis of symptoms, with Tamiflu vouchers being handed out to “flu friends” of those infected. High-risk groups, including babies and pregnant women, are still seen at doctors’ surgeries. As the treatment phase develops, not everyone will receive Tamiflu, which may be reserved for such at-risk groups, as well as people with chronic diseases, the under 5s and the elderly. The tracing of contacts and treating of people as a precaution stops completely. The National Pandemic Flu Service goes active, with diagnosis via central call centres, and use of unique reference numbers given to patients. Tamiflu can be collected from up to 500 antiviral collection points, or ACPs, around the country. The Government takes the lead, and the NHS follows its directives.

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