Chief medical officer Sir Liam Donaldson has described the rise in new swine flu cases as a "small increase".
Around 84,000 people contracted the disease during the last week, which is a rise of just 6,000 from the preceding week.
The increase is moderate compared to previous weeks, and could be attributed to the national half-term school break, Sir Liam said.
"This could be a half-term effect - we can't be completely sure - so, before starting to talk too much about the overall flattening off and even a slight reduction, we've got to wait a week or two to see what happens," he said via video link from Washington in the US.
But the number of patients admitted in critical care due to swine flu increased. Of the 848 people in hospital with the virus, 172 are in intensive care.
Sir Liam said this increase is putting "pressure on hospital services".
"There has been a snowballing of cases in intensive care over the last few weeks, which is giving us concern."
The total number of deaths in the UK is now 154, with England recording 105, eight in Wales, 31 in Scotland and 10 in Northern Ireland.