The number of people known to have died after contracting swine flu has doubled in three days. Fourteen people have died in Britain after testing positive for the H1N1 virus.

London and the West Midlands have emerged as hotspots after a marked rise in the number of suspected cases this week.

In England and Wales, 27,000 people contacted their GP about “flu-like illness” in a single week, the latest figures suggest. It is estimated that, of these, 8,000 would have swine flu.

The Health Protection Agency also disclosed that at least 335 people were having hospital treatment for serious infections, of whom 43 were receiving “critical care” as of yesterday. Sixty of those in hospital were aged under 5, and 47 were aged between 5 and 15. There were 189 aged between 16 and 64, and only 39 over 65.

Britain now has the third-highest number of confirmed cases of swine flu in the world after the US and Mexico, where the pandemic originated.

But exact figures for the numbers of people with a diagnosis of swine flu in Britain are no longer being given because of the large numbers infected.

Sir Liam Donaldson, the Chief Medical Officer, said that every day thousands of people were seeking medical help but that the number of cases being diagnosed by GPs was the “tip of the iceberg”, because many people would not be contacting their doctor.

The latest estimate, based on a sample of GP practices, is equivalent to a rate of 51 people complaining of flu symptoms for every 100,000 people in England and Wales.

Sir Liam said that the health service was coping well with outbreaks of illness since most cases were mild and did not require medical treatment.

The worst-hit areas are London and the West Midlands, both showing nearepidemic levels of infection — defined as 200 cases per 100,000 population.

Sir Liam said: “Even with seasonal flu, you start to see different parts of the country affected in sequence. I’m convinced when we do see a big surge it will sweep around the country.”

Of the 14 deaths, 12 occurred in England and two in Scotland. Justin McCracken, chief executive of the agency, said that it was a local decision in each case whether to release details of where and who the victims were.

Last week the Government announced a shift from containment strategy to a treatment phase, which means cases are no longer confirmed in a laboratory. The number of cases is monitored in various ways, including laboratory testing on sample groups, surveying some GP practices and counting calls received by NHS Direct.

Sir Liam acknowledged that the true number of people with swine flu was unknown. “We know something about the people seeking help from the NHS but there will be many other people who look after themselves or don’t realise they have it and don’t show up. We have to acknowledge the problem is bigger than surveillance is showing us. That will always be the case — it would be the case with anything.”

Explore Health

• Expert Advice

• Health Features

• Mental Health

• Alternative Medicine

• Child Health

• Health Club