New cases of swine flu could top more than 100,000 a day by the end of August, ministers have warned, as they admitted they can no longer contain the spread of the virus.

Patients with suspected symptoms will now be told to stay at home and telephone their family doctor for a diagnosis, as part of a major step change in the handling of the pandemic, in an effort to limit the spread of the infection.

Anti-viral drugs will also no longer be given as a precaution to people who may have come in contact with the infection.

Andy Burnham, the Health Secretary, said that an almost doubling of cases over the past seven days had prompted the Government to move to the third and final “treatment” stage of dealing with the outbreak.

A specially convened meeting of Cobra, the Government’s emergencies committee, was warned that cases could reach 100,000 a day by late August.

Although he insisted that this was merely a “projection” if the virus continues to spread at its current rate, Mr Burnham added: “The pressure on the system is such that it is the right time to take this step”.

The projection raises the possibility that millions of people will have had the virus even before the start of the traditional flu season.

Although the first doses of a vaccine against the virus are also due by August most will not arrive until the end of this year or next year.

The total number of recorded cases has jumped from 3,500 last week to more than 7,400.

Although most people have developed relatively mild cases of the flu, three patients with underlying health problems have died in Britain.

The latest move comes just a week after the Department of Health moved to the second stage of its plan to deal with flu.

From now on cases across the country will no longer have to be diagnosed by a laboratory but will be done by GPs over the telephone.

People who suspect that they might have the infection are asked to check their symptoms against a list on the NHS website before they ring their local doctors’s surgery.

The closure of schools to contain outbreaks is no longer recommended, although officials said that the coming summer holidays could help to reduce the number of new cases.

Patients with symptoms will still be given anti-viral drugs which can help them recover more quickly and limit spread of the infection.

However, Mr Burnham said that scientific evidence suggested that if the flu continues to spread the drugs, including tamiflu, might be restricted to high risk groups, such as the elderly and pregnant women, to prevent problems caused by overuse.

Some flu “hot spots” are due to set up “collection points”, where affected patients can remain at home and appoint a friend to pick up their drugs for them.

A national telephone flu line, in which patients would be diagnosed through a central call centre, could be set up “within weeks” if the virus continues to spread at the same rate.

An end to laboratory testing will mean that daily running totals of the numbers affected will be replaced by weekly estimates.

Andrew Lansley, the shadow health secretary, warned that infection rates of 100,000 could lead to around 2,000 hospital admissions a day, placing hospitals under pressure.

But Prof Sir Liam Donaldson, the Chief Medical Officer, insisted that the NHS was well prepared to cope with the worst-case scenario and that the virus was following a predictable course.

He added that data from across the world on the severity of the virus was still too limited to make an accurate prediction of death rates.

Mr Burnham added: “We are in a strong position to deal with this pandemic. We are the only country in the world to be able to offer anti-virals to everyone as well as those at greater risks. People should be reassured and should not be alarmed by this change.”

London, the West Midlands and Scotland have been particularly affected by outbreaks of the virus so far.

More than 77,200 people across the world have been infected with swine flu since April and there have been 332 deaths.

By Kate Devlin, Medical Correspondent
Published: 7:00AM BST 03 Jul 2009