More than a quarter of people living with HIV are unaware that they have the infection, figures have suggested.
An estimated 86,500 people in England had HIV in 2009 but almost 22,500 were undiagnosed, according to data from the Health Protection Agency (HPA).
The HPA has called for more widespread testing after its figures showed 52% (3,450) of new cases in 2009 were diagnosed late - after a time when treatment could have started.
Overall, there were 6,630 new cases of HIV last year with 4,400 men and 2,230 women contracting the disease.
Figures showed that the number of new cases fell for the fourth year in a row, but the proportion of undiagnosed cases has not changed in the last decade.
The HPA said more widespread testing was especially needed in areas where the number of new cases is above two people per 1,000 population.
Of 37 health trust regions across England with levels above this, 26 are in London.
Across the UK, 1.4 people per 1,000 of the population have HIV, whether diagnosed or undiagnosed.
In the capital, 5.24 per 1,000 people had a diagnosed HIV infection in 2009, while Brighton and Hove had a rate of 7.57 per 1,000 people and in Manchester the rate was 5.22 per 1,000 people.
Health officials said those most at risk included gay men and black Africans.
Dr Valerie Delpech, consultant epidemiologist and head of HIV surveillance at the HPA, said: "The HPA would like to see increased access to HIV testing in areas where rates of HIV infection are high.
"Pilot studies have shown that in these areas testing all adults registering at GPs or accessing certain hospital services can make an impact.
"The evidence shows that this testing is feasible to undertake and acceptable to patients."
Copyright © Press Association 2010
<http://www.hpa.org.uk/> (Health Protection Agency)
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