The Government has signed contracts for up to 90 million doses of a pre-pandemic swine flu vaccine, as the total number of UK cases reached 85.
Three new cases were confirmed in Scotland this afternoon, followed by the another four confirmed cases in schoolchildren in London.
The new contracts, between the Government and GlaxoSmithKline (GSK) and Baxter, means work can start on a vaccine before any pandemic begins.
By December this year, the UK would have enough pre-pandemic vaccine to protect at least half of the population from swine flu.
However, if the World Health Organisation (WHO) declares a pandemic before then, another contract would come into force which allows production of a pandemic swine flu vaccine.
The vaccines would almost certainly be the same unless the strain mutates sufficiently to require an entirely new vaccine to be made.
The Department of Health said today's agreement could provide enough vaccine to protect the most vulnerable people before a pandemic arrived, without affecting the normal supply of seasonal flu vaccine.
Health Secretary Alan Johnson said: "The localised cases of swine flu found in the UK have so far been mild, and our strategy of containing the spread with anti-virals appears to have been effective in reducing symptoms and preventing further spread of infection.
"Scientists tell us that, as yet, we don't know enough about this novel strain, or whether it's likely to mutate, but that this virus has the potential to become a pandemic and we can't predict how serious that would be.
"We have an opportunity to secure vaccine in advance of a pandemic wave. We have advance purchase agreements to provide vaccine for the entire UK population which will take effect when phase 6 pandemic is declared.
"It will then take over a year for all the vaccine necessary to be provided.
"These additional arrangements provide the opportunity by December this year to have enough pre-pandemic vaccine to protect at least half of the population from swine flu.
"This will, however, depend on when and if the manufacturers switched from seasonal to H1N1 pandemic specific vaccine production at a time after phase 6 is declared by the World Health Organisation, as this will take precedence over pre-pandemic contracts."
Once a pandemic is declared, the contract signed by GSK, Baxter and the Government in 2007 allows for up to 132 million doses of a specific pandemic flu vaccine.