Each year, the WHO selects strains known to be circulating for inclusion in the winter flu vaccine.

CMO for England Sir Liam Donaldson said last week it was 'likely' that the swine flu virus would be among the strains selected in future years.

But he added: 'If we get the vaccination rates up, then, obviously, it will be less of a threat in future years than it is this year.'

The adjuvanted vaccine used in the UK will mean that this year's swine flu jabs will offer cross-protection against strains in future years if the virus mutates, Sir Liam said.

That means that, unlike seasonal vaccines, this year's swine flu vaccine provides protection for more than one year.

Sir Liam also revealed figures showing that consultations and estimated cases of swine flu have fallen, but the number of deaths from the virus has risen relatively sharply.

So far, there had been 182 confirmed deaths during the outbreak, a rise of 28 from the previous week, he said.

The overall fall has occurred in the face of a rise in cases in children and older patients, Sir Liam added. 'For the first time, we are seeing quite an upturn in the older age groups, 65-74-year-olds and over 75s.'