Many people are unaware they are infected
More people than ever before are living with HIV in the UK but more than a quarter do not know they have it, figures show.
The number of estimated cases rose by 8% between 2007 and 2008, says the Health Protection Agency.
But it is thought 22,000 of the 83,000 people with HIV do not know they are infected.
The Terrence Higgins Trust said the high levels of undiagnosed HIV were "completely unacceptable".
In its annual HIV report, the HPA said they expected the number of people living with the infection to continue to rise as people live longer on effective therapy.
There has also been an increase in testing with 100,000 more tests done at sexual health clinics in 2008 than the previous year.
Late diagnosis is also a problem with 32% of adults in 2008 diagnosed past the point at which treatment should already have begun.
Guidelines from the British HIV Association introduced last year, suggest even stronger targets, recommending patients are considered for treatment when their CD4 immune cell count reaches less than 350 per mm3 rather than waiting until it falls further to less than 200 per mm3.
Under these rules, more than half of new cases last year would have been diagnosed late.
In 2008, 7,300 people were diagnosed with HIV and gay and bisexual men are still one of the highest risk groups for infection, although new infections in this group has fallen from the previous year.
The figures also show that 58% of new diagnoses were among heterosexuals, two-thirds of whom were Black Africans who are likely to have acquired the infection abroad.
But the proportion all new heterosexual diagnoses acquired in the UK is steadily rising
In 43 local authorities in England with higher than average HIV rates, health professionals should routinely offer testing to all men and women aged 15 to 59 years who are registering in general practice or admitted for medical care.
Dr Valerie Delpech, an expert in HIV from the Health Protection Agency said: "HIV is a serious infection but if diagnosed early, there are very good treatment options.
"Of concern is that over 22,000 people remain unaware of their infection in the UK and cannot therefore benefit from effective treatment.
"We need to continually reinforce the safe sex message - using a condom with all new or casual sexual partners is the surest way to ensure you do not become infected with a serious sexually transmitted infection such as HIV."
Sir Nick Partridge, chief executive of the Terrence Higgins Trust said: "The level of undiagnosed HIV in the country is completely unacceptable.
"With early diagnosis and effective treatment, most people with HIV can live to old age.
"If left undiagnosed, they will die earlier, be significantly more ill and more likely to infect others."
He called for more testing in more settings with the introduction of a national targeted screening programme to halve undiagnosed HIV in the UK by 2014.
Deborah Jack, chief executive, at the National AIDS Trust said the UK had not succeeded in turning the tide on HIV.
"Instead we continue to see high numbers of gay men being diagnosed and a growing number of heterosexuals infected within the UK.
"Preventing just one HIV infection could save over a quarter of a million pounds, yet over the past ten years HIV has been politically sidelined in the UK and spending on prevention at a local level has been cut."