Fourteen people are now thought to have died in the UK after contracting swine flu, the Government announced today.

Chief Medical Officer Sir Liam Donaldson said the latest figures did not mean they all died as a direct result of swine flu but that many had the virus.

There are currently 335 people in hospital in England with swine flu of which 43 are in critical care, he added.

The UK now has the third highest number of cases of swine flu in the world after the US and Mexico.

However, Sir Liam admitted it was unknown how many people in the UK were truly suffering from the virus as many people would be treating themselves at home rather than contacting their GP.

It is unclear where or when the latest deaths linked to swine flu occurred.

Justin McCracken, chief executive of the Health Protection Agency (HPC), said the organisation would not be releasing information about individual deaths, adding that it was a local decision in each case whether to release details of where and who the victims were.

Sir Liam said latest data from 100 GP surgeries around England showed that about 27,000 people per week were being diagnosed by their GP as having a flu-like illness.

Of these, an estimated 8,000 will have swine flu.

As of yesterday there were 9,718 confirmed cases of swine flu in the UK. This was just behind Mexico, with 10,262 cases. The US currently has 33,902 confirmed cases.

However, cases of swine flu in the UK are no longer being diagnosed by laboratory testing as the virus continues to spread. Of the 14 deaths, 12 occurred in England.

Sir Liam said today that London and the West Midlands were approaching epidemic levels in terms of the number of cases being seen.

The number of cases is now being monitored in various ways including laboratory testing on sample groups, some GP practices and the number of calls received by NHS Direct.

However Sir Liam acknowledged that the true number of people with swine flu was unknown.

"We do know something about the people seeking help from the NHS but there will be many other people who look after themselves, don't realise they have it and don't show up.

"We have to acknowledge the problem is bigger than surveillance is showing us."

He continued: "That will always be the case, it would be the case with seasonal flu or anything else."

Last week Health Secretary Andy Burnham said estimates were that 100,000 new cases of swine flu could occur in the UK by the end of August.

Sir Liam said that was the most accurate prediction to date of what will happen.

It is widely expected that the number of cases will see a surge in the winter months when flu is more prevalent.

Sir Liam explained that the Government was also using a system called QSurveillance to monitor the situation.

This automatically draws data on a daily basis from GP electronic records.

About 15 per cent of calls to NHS Direct are currently about colds and flu, he added.