The government hopes to provide anti-flu drugs for 80% of the population.
Another 149 cases of swine flu have been confirmed in the UK, bringing the total to more than 2,900.
More than 100 patients under observation in England were confirmed with the virus on Tuesday, along with another 40 cases in Scotland.
The number of confirmed cases in the UK is 2,944, including 686 in Scotland.
The Health Protection Agency said a baby from County Durham has tested positive for swine flu at a hospital on Teesside and is in a stable condition.
About 30,000 cases of swine flu have so far been detected in 74 countries, and more than 140 people have died worldwide since March.
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."
The swine flu virus claimed its first victim in the UK last week, after a female patient died in a Scottish hospital.
The victim was a woman aged 38 who gave birth prematurely while being treated at the Royal Alexandra Hospital in Paisley.
The baby with swine flu is aged less than a year and has been admitted to North Tees Hospital, in Stockton, and given anti-viral drugs.
As a precautionary measure, family members and staff who were in close contact with the baby have also been offered the Tamiflu drug.
The baby's condition was said to be stable.