Estimates suggest the age range between 15 and 44 is the most severely affected, with 24.3 per cent of laboratory samples from this group testing positive, according to the UK Health Security Agency.
Samples from all age groups testing positive are at 14.3 per cent in the week to December 4, up from 12.5 per cent the previous week.
Hospital admission rates are highest for those aged between 75 and 84, at 9.3 for every 100,000 people, followed by children under five (6.6) and over-85s (6.5).
The overall level of flu is still estimated to be below the same point three years ago, in the pre-Covid winter of 2019-2020.
Staying safe during flu season - in pictures
Inoculation among those aged between two and three is eight percentage points lower than last year and just over 14 points below the equivalent level in 2020-2021.
Just over a third (35.4 per cent) of two-year-olds have received a flu vaccine, along with a slightly higher proportion (37.6 per cent) of three-year-olds.
All children aged two and three are eligible for a flu nasal spray vaccine, which is being offered by local GPs.
In total, about 33 million people in England can have free flu vaccination this year, including everyone aged 50 and over, all primary school-aged children and some secondary school-aged children.
The vaccine is also being offered to pregnant women, people in care homes, frontline health and social care staff, carers, those aged six to 49 with a specified health condition, and household contacts of people with weakened immune systems.
Flu vaccination being administered around the world - in pictures
“With winter now upon us, we are seeing flu circulating more widely," said Dr Conall Watson, the health agency's consultant epidemiologist.
“The NHS [National Health Service] frontline has already delivered millions of vaccines to those most at risk from what can be a deadly virus.
"With Christmas fast approaching, if you are eligible and have not yet been vaccinated, it can take a fortnight or so for the flu vaccine to provide protection.
“Nobody wants to see their loved ones sick or in hospital with flu over Christmas, so to ensure your family are ready to enjoy the festive season together, don’t hesitate and book your vaccine today.”
Flu and the common cold – in pictures
Figures from NHS England show there were an average of 712 flu cases a day in hospitals last week, up 48 per cent from 482 the previous week.
The figure for the first week of December last year was 31.