Pregnant women and people with weakened immune systems could be advised to stay away from crowds for a period of a "few weeks" should the swine flu reach "big numbers" in the autumn, the chief medical officer has said.
Sir Liam Donaldson said pregnant women were not currently being advised to cut down on their normal daily activity but there was a possibility that he could issue such advice in the autumn if swine flu reached a level of, for example, one in three of the population.
"We are not advising pregnant women to cut down on their normal daily activity - some might choose to be very precautionary and not want to go into crowded places, but that is not the advice," he told GMTV. "But we will look at it again when it comes to the autumn when we get possibly big numbers of cases.
"If we got, for example, one in three of the population affected by flu which is one of the estimates, at that point I may advise pregnant women and people for example on cancer treatment who have weakened immune systems to avoid crowded places for a period of a few weeks when it is at its peak."
Sir Liam reiterated advice for pregnant women who believe they have the symptoms of swine flu to contact their GP. He added that pregnant women should stay away from friends or neighbours suspected of having the virus or who have it and be "extra cautious" in washing their hands after being out when, for example, using public transport.
He said at the moment there was not enough swine flu "out there" for people to have a "big chance" of encountering the virus on a daily basis.
His comments come after Health Secretary Andy Burnham sought to reassure pregnant women amid accusations of conflicting advice on how they should behave during the swine flu epidemic.
In a statement to MPs, Mr Burnham insisted the Government's advice to expectant mothers had not changed.
Most pregnant women with swine flu will only get mild symptoms and they should continue normal activity such as going to work, travelling on public transport and attending events and family gatherings, he said.
But owing to a higher possibility of complications, he said they should wash their hands frequently with soap and water and avoid contact with people who have swine flu.