An "increasing pool" of people in the UK are living with HIV and Aids, official statistics show.
People with HIV are living longer thanks to improved treatments
The Health Protection Agency says around 63,500 UK adults were living with HIV in 2005 - with as many as a third unaware of their infection.
Most new HIV cases in 2005 were infected abroad, but more cases are being contracted in the UK, it said.
However, the HPA figures show a relatively small increase in new HIV diagnoses, compared to previous years.
The total number living with HIV in the UK in 2004 was 58,300.
The figures show there were 7,450 diagnoses in 2005, compared to 7,275 revealed in last year's HPA report.
Two thirds of all new cases diagnosed last year were in people who contracted HIV in other countries where the virus is more prevalent, such as sub-Saharan Africa.
A third were among gay and bisexual men.
However, the increase among that group was small with an increase of around 50 new diagnoses compared to 2004.
Dr Valerie Delpech, an HIV expert at the HPA said: "We are seeing an ever increasing pool of people living with HIV and Aids in the UK.
"This is due to people living longer with HIV due to advances in treatment, sustained levels of newly acquired infections in gay men, further diagnoses among heterosexuals who acquired their infection in Africa, and cases being picked up earlier."
She added: "Despite some improvements we are also concerned that many HIV infections are still being diagnosed late, so that life expectancy is reduced as treatment is not begun when required."
Will Nutland, of the Terrence Higgins Trust, said: "Over the last five years, we have seen some very steep increases in new HIV cases.
"Whilst figures have risen this year, the rate of acceleration of increase is much slower."
"Over two-thirds of diagnoses we see are from people who acquired their infection outside the UK.
"A third are men, gay and bisexual, most of whom acquired HIV in the UK.
"They are the most vulnerable group within this country."
Deborah Jack, chief executive of the National Aids Trust said: "HIV testing should be made more widely available outside GU and antenatal clinics in order to reduce the high level of people living with HIV who are undiagnosed or diagnosed late.
"This must be coupled with initiatives to tackle stigma and educate the public about HIV as ignorance and discrimination can act as a barrier to people getting tested."
The HPA figures also show a rise in sexually transmitted infections.
In 2005, 790,443 STIs were diagnosed in clinics in the UK compared to 767,785 in 2004.
Men who have sex with men, and young people appear to be at particular risk.
Gonorrhoea diagnoses fell by 13% from 22,321 in 2004 to 19,392 in 2005, but incidence remained high in men who have sex with men.
Syphilis cases increased by 23%, from 2,282 to 2,814 with most cases also seen in men who sleep with men.
Three quarters of chlamydia cases were diagnosed in 16 to 24-year-olds.
Anne Weyman, chief executive of the FPA (Family Planning Association) said: "There is a human cost of complacency in not tackling the ignorance, fear and embarrassment which stops people from coming forward for STI testing - including HIV, and prohibits health professionals from proactively targeting the groups most at risk."
Public health minister Caroline Flint said: "We are seeing an increase in the number of people with HIV partly because more people are being encouraged to come forward for testing and also people diagnosed with HIV are now living longer healthier lives thanks to more effective treatments.
"However, tackling the rise in STIs, including HIV, is a key priority for the government which is why we are investing record amounts of money in this area.
"A new £4m sexual health campaign was also launched this month to tackle the spread of major acute STIs."