Twenty-eight per cent of people living with HIV in the UK are unaware they are infected, the Health Protection Agency has said.

An estimated 77,400 people in the UK are thought to have HIV, up from an estimated 73,000 in 2006.

The agency said there were 7,734 new diagnoses of HIV in 2007 but almost a third of people are being diagnosed late, after the stage at which they should have begun drug therapy for the condition. It said testing needed to be more widely available to reduce transmission rates in the heterosexual and homosexual populations.

"It is very worrying that so many people remain unaware of their HIV status. Wider HIV testing in high prevalence areas of the UK is urgently needed," said HPA Centre for Infections head of HIV surveillance Valerie Delpech.

Prevalence is greatest in London, parts of the south coast, Manchester and Blackpool.

Of new diagnoses in 2007, 41 per cent were among gay men, the majority of whom had become infected in the UK, and 55 per cent were acquired through heterosexual contact. The majority of the latter were probably acquired abroad.

A total of 180 new infections were acquired through injection drug use and 110 through mother to child transmission.