The government hopes to provide anti-flu drugs for 80% of the population
The number of confirmed swine flu cases in England has jumped by nearly 20% in a single day, latest figures show.
The Health Protection Agency statistics show that 535 new cases were confirmed on Friday, bringing the total to 3,364.
Scotland registered another 72 cases on Friday, an 8.5% rise, bringing the total to 922, and a 25th case was confirmed in Northern Ireland.
With 12 cases confirmed in Wales, the total number of confirmed UK cases now stands at 4,323.
Sir Liam Donaldson, the chief medical officer for England, warned on Thursday that the UK could soon expect to see a surge of new cases.
He predicted tens of thousands of cases of swine flu could be emerging each week by the autumn.
The West Midlands remains the most badly affected area of England, with 158 new cases confirmed on Friday, bringing the total to 1,516.
Some hospitals in that region have created triage areas to cope with complaints of symptoms.
London is the other swine flu "hotspot" in England, recording 225 new cases on Friday, taking the total to 985.
Change of policy
Officials in both areas announced on Thursday they had abandoned attempts to contain spread of the virus, instead opting for a policy of managing the outbreak.
The containment policy involved trying to ring-fence outbreaks by tracing the people with whom confirmed cases have come into contact and giving them drugs to try to prevent flu developing.
This approach has also involved the closure of several schools.
But once the virus starts to spread freely in a community that policy becomes impractical.
At this stage, anti-viral drugs are only given to those people showing symptoms, and tracing of contacts is abandoned.
The practice of waiting for laboratory confirmation of new cases is also scrapped in favour of clinical diagnosis based on symptoms.
A Department of Health spokesman said: "The cases of swine flu found in the UK have so far been generally mild in most people, but are proving to be severe in a small minority of cases.
"We are continuing to work to slow the spread of the disease and to put in place arrangements to ensure that the UK is well-placed to deal with this new infection."
Sir Liam said on Thursday that the UK was likely to receive its first batches of swine flu vaccine in August, rather than in the autumn as first expected.
The government has contracts with two manufacturers for 132m doses - enough for the whole population.