Record numbers of people in the UK are living with HIV, with more than half of newly diagnosed infections found in heterosexuals, figures revealed today.

The Health Protection Agency (HPA) said that in 2007 an estimated 77,400 people had the virus, up from 73,000 in the previous year. More than a quarter of those infected remained unaware of their status.

During 2007, 7,734 new cases of HIV were found, including in 3,160 gay men and 4,260 heterosexual men and women.

The estimated number of people infected through heterosexual contact in the UK jumped from 540 in 2003 to 960 in 2007, figures show.

Almost a third of people who found out they were infected were diagnosed late, at a point after which treatment should have begun. They risked losing benefits associated with early diagnosis, including prolonged life expectancy.

Valerie Delpech, the head of HIV surveillance at the HPA's Centre for Infections, said: "Diagnosing HIV infections earlier will reduce transmission of this infection as those unaware of their positive status pose a greater risk to future sexual partners. Late diagnosis also has a major impact on disease and life expectancy and it is vital that people are diagnosed early.

"It is worrying that so many people remain unaware of their HIV status. Wider HIV testing in high prevalence areas of the UK is urgently needed to reduce the number of undiagnosed infections."

Lisa Power, head of policy at the HIV charity Terrence Higgins Trust, said: "There are now well over 20,000 people in the UK who have HIV and don't know it. Not only is this dangerous to their own health, but they are more likely to pass the virus on than someone who has been diagnosed."

New guidelines recommend wider HIV testing in areas of the country where the prevalence of the virus is greatest, such as London, Manchester and parts of the south coast.

Delpech said: "Access to testing must be made easier. We need to improve availability of HIV testing in a number of healthcare settings, including general practice, to improve diagnosis of this infection. Without this we will not see the reduction in transmission that we need to see, or a further fall in serious disease."