The number of people contacting their doctor over fears they have swine flu has jumped almost 50% in the last week to 40,000 a week, figures have shown.
More than 73 people per 100,000 reported flu-like illness from 6-12 July - up 46% on the week before, the Royal College of GPs said.
The figures for England and Wales also showed those aged five to 14 had the highest rate, at 159.57 per 100,000.
Youngsters and babies aged up to four were next at 114.12 per 100,000.
These were followed by people aged 15 to 44, those aged 45 to 64 and then the 65 and overs.
The weekly report from the college's monitoring system said: "National incidence of influenza-like illness increased for all regions and is now evident in all age groups."
Central England has the highest number of cases at 94 per 100,000, but the North had witnessed "a marked increase" on previous weeks, up from 6.6 to 37.16 in just one week.
London had seen a small drop in cases but remained a major hot spot for the virus.
The figures, based on a sample of 84 GP surgeries across Britain, are used by the government to monitor the flu pandemic.
Flu kills between 5,000 and 7,000 people in a typical winter - mainly the elderly - although the number can rise to more than 10,000 in bad years.
Experts are concerned the H1N1 swine flu strain is affecting younger people.
The swine flu vaccine is expected to arrive in the UK at the end of August, the government has said, with a priority list for those most in need.
They include people aged six months to 65 with a health condition like asthma, diabetes, heart, liver or kidney disease, or a suppressed immune system.
Pregnant women in their second or third trimester are also on the list, as are frontline health workers and children aged three to 16.
The UK is due to receive around 60 million doses of the vaccine - enough to cover half the population - by the end of December. The rest will follow next year.
However, the jab has still to be approved by various regulators, which could delay its distribution.
The number of UK deaths linked to the virus stands at 17.
Published: 2009/07/15 21:12:17 GMT