More than 300 people are in intensive care with flu, Government figures have shown.
Data from the Department of Health for England revealed there were 302 people in intensive care beds. It is unclear how many have swine flu but they are expected to be in the majority.
New figures on the number of deaths from flu and swine flu will be released by the Health Protection Agency on Thursday.
Health Secretary Andrew Lansley briefed Cabinet colleagues on Tuesday morning on the flu situation and told them the NHS had plenty of capacity to deal with the upsurge in cases.
Prime Minister David Cameron told a press conference at 10 Downing Street: "We had a report at Cabinet this morning from the Health Secretary about the situation as regards flu, and particularly swine flu.
"He gave a report about the number of critical care beds being used for people with flu. While obviously the number of flu cases has doubled in the last week, there is still plenty of capacity in the NHS.
"I think the figures on flu are are quite similar to two years ago. They are a little worse than last year. I think there is a very good grip in the Department of Health on this issue. Andrew Lansley has a great grip over that department."
Mr Cameron said he did not know whether his wife Samantha had been advised of the risk of swine flu to pregnant women while she was carrying their fourth child, Florence, who was born earlier this year.
As of Monday, there were 24 children under five in critical care with confirmed or suspected flu, another 12 aged five to 15, and 243 in the 16 to 64 age group. There were also 23 people aged over 65 in critical care.
So far this flu season, 14 people have died with confirmed swine flu and another three from flu type B. Of those who died, all were aged under 65, with six aged under 18.