Britain is to change the way it deals with the H1N1 flu outbreak after projections that over 100,000 new cases a day could be emerging by the end of August.

Faced with such huge numbers, the focus will switch to treating the disease rather than trying to contain it.

Confirmed cases are doubling every week, putting pressure on health services, Health Secretary Andy Burnham said on Thursday.

"On this trend, we could see over 100,000 cases per day by the end of August -- though I stress this is only a projection," he told the House of Commons.

The first doses of a pandemic flu vaccine would arrive in Britain by the end of August, with 60 million doses available by the end of the year, enough for 30 million people, or about half the population.

Most people who have caught the infection have only suffered mild symptoms, but in a small minority it has proved more severe, with three deaths in Britain so far.

"We have always known it would be impossible to contain the virus indefinitely and that at some point we would have to move away from containment to treating the increasing numbers falling ill," Burnham said.

Health officials will target antivirals at the most vulnerable, who should contact their GP as soon as possible if they think they have H1N1 flu.

These include all those with certain long term conditions, compromised immune systems, people over 65, pregnant women and children under five.

Antivirals will continue to be offered to patients with the flu or showing symptoms, although it will remain at the discretion of doctors whether to prescribe them.

"I know that local GP surgeries and hospitals are coming under increased pressure," Burnham said. "It's important we do everything we can to reduce the strain on local health services."

Attempts to trace people who have been in contact with flu sufferers would now stop.

Health authorities will also no longer compile daily updates on the number of new cases, with estimates of the general spread being issued instead.

People concerned they have caught the H1N1 flu should check the NHS website or call the Swine Flu Information Line on 0800 1513513.

If still concerned, they should contact their family doctor, who will diagnose them over the phone, rather than waiting for a laboratory confirmation.

If the infection is confirmed, the doctor will issue an authorisation allowing a "flu friend" to collect antivirals from a collection point at a pharmacy or a community centre.

Later, all diagnosis will be done by a national swine flu service, with authorisation for antivirals issued online or through a call centre.

Public health experts backed the changes. "It's a much more sensible approach," said Alan Maryon Davis, president of the Faculty of Public Health.

"It means we can conserve the antiviral stocks that we have got, just in case the virus comes back with a vengeance later in the year," he told BBC television.

There are now 7,447 confirmed H1N1 flu cases in Britain, with infections spreading fastest in the southwest, the east, the east Midlands and in London, which all saw more than a three-fold increase over the past week.