A 19-year-old man has become the fourth person in the UK to die after contracting swine flu, health chiefs said today.

The teenager from south London, who had serious underlying health problems, tested positive for the virus following his death on Wednesday and is the first person to die with swine flu in the capital.

His death comes amid warnings that the number of cases could soar to 100,000 a day by the end of next month.

Health chiefs said the UK has moved past the stage of containing the outbreak and into the "treatment phase".

Dr Simon Tanner, regional director of public health for London, said: "It's with sadness that we have to announce the death of a patient in London who has subsequently tested positive for H1N1 swine flu."

He said his thoughts were with the man's family and no further details about the patient would be released.

London, along with the West Midlands, is a swine flu hotspot and Dr Tanner said everyone had a responsibility to "catch it, bin it, kill it" to protect the vulnerable.

"There are people out there in the community, and we've talked about one today - precious individuals that have got really difficult medical conditions - who are particularly vulnerable when the population has a virus like this in it," he said at a briefing in central London.

"We've all got a responsibility for their sake.

"We would make the judgment that a major conurbation, with a lot of people coming into it every day, with lots of people working in close proximity, is likely to be the sort of area where you would see the spread of any infectious disease."

But he added: "It's not completely clear as to why we saw the hotspots that we have seen."

He said most of the confirmed cases showed mild symptoms, but added: "Some people may be more susceptible to the virus and if you have flu-like symptoms, it is important that you talk to your doctor."

It is understood the 19-year-old was taken to hospital in Lewisham.

Three other people with swine flu have died in the UK and all had underlying health problems.

Jacqui Fleming, 38, of Glasgow, was the first after contracting the virus last month, two weeks after her son, Jack, was born 11 weeks prematurely. Jack died later but had not contracted the virus.

The second victim was a 73-year-old man from the Inverclyde area of Scotland.

Then a week ago, six-year-old Sameerah Ahmad became the youngest UK victim to date.

Sameerah, who was born with a rare life-threatening disease, died at Birmingham's Children's Hospital after contracting swine flu, although it is unclear if it contributed to her death.

The Government has signed contracts with GSK and Baxter for the supply of 130 million doses of swine flu vaccine - enough for the entire population.

The first delivery is expected next month, and 60 million doses should have been delivered by the end of the year.

The remaining doses will not arrive until next year.

It is not clear who will be given the vaccine first but health workers and at-risk groups - such as people with heart disease, diabetes or asthma, and children aged under-five - are likely to be the priority.

Earlier today the Government's chief medical officer warned the public to avoid panic-buying "counterfeit" anti-swine flu drugs online.

Sir Liam Donaldson said there was no need for people to resort to the internet to self-medicate.

He said Britain had a massive stockpile of Tamiflu and would be one of the first countries to have access to a vaccine, with the first supplies arriving at the end of next month.

Sir Liam told GMTV: "There's generally a growth in people ordering drugs from the internet worldwide and there's a lot of concern among health authorities that people might buy counterfeit drugs.

"I think this is a similar situation - people shouldn't buy Tamiflu from the internet.

"We have got a massive stockpile in this country and everybody can have access to it through the National Health Service."

Sir Liam added he was "surprised" health services controlled the virus for as long as they had. The first case in Britain was recorded in April.

He said: "We have been dealing with it very aggressively so far - we have investigated every case, we've treated their contacts, we've closed schools and all of that has helped slow the spread.

"We are surprised we have been able to run it as long as we have like this. Flu viruses spread extremely quickly so this is very much going as expected."

Meanwhile, eight British school students have been hospitalised in northeast Romania with swine flu, an embassy official said.

Embassy communications officer Raluca Bragarea said the group arrived in Romania on June 25 as part of an annual exchange programme to work with disabled children in the northeast city of Iasi.

The British teenagers, aged between 16 and 18, are in a group of 19 students and three teachers from the private Sevenoaks School in Kent.

They are currently in isolation at Iasi's Hospital for Infectious Diseases and British diplomats are liaising with the school and Romanian public health authorities to decide whether to fly the students home or keep them in the hospital.