The number of new cases of HIV diagnosed in the UK has risen by 20% in one year, according to figures released today by the Health Protection Agency.

There have been 5,047 new cases so far for 2003, compared with 4,204 at the same time last year. Increases in people having unsafe sex were "undoubtedly the main driving force" behind the figures, the HPA said

Infection with HIV was increasing in both gay and heterosexual people. But the sharpest increase in new cases for 2003 was among heterosexuals - up from 2,199 to 2,785.

There were 1,414 new diagnoses among gay men in 2003, with the figure expected to rise to more than 2,000 when all reports are received. That compared with 1,195 reported at this time last year for 2002.

Dr Barry Evans, an HIV expert at the HPA, said: "The year on year increase we are observing in the number of newly diagnosed HIV infections is a cause for considerable concern.

"When all reports have been received we expect the total for 2003 to be the highest ever at over 7,000. HIV is an infection that is here to stay."

He said with almost a third of the 49,500 people currently living with HIV in the UK still unaware they are infected, the rising trend in new diagnoses is liable to only get worse before it gets better.

Some of the increase he said could be related to the rise in other sexually transmitted infections, which can aid the transmission of HIV, or people coming forward for HIV testing who may have been infected for sometime .

But he added: "Increases in unsafe sex are undoubtedly the main driving force behind this epidemic."

Changing people's sexual behaviour so they use a condom with all new and casual partners was one of the most effective ways of reversing the trend, he suggested.

Nick Partridge, chief executive of Terrence Higgins Trust, said: "We've been talking about the HIV and sexual health crisis for the last year. Now it's time for action.

"Modernising sexual health services to make it easier for people to test for HIV and other STIs would be a major step forward in helping to tackle this crisis. We must also make a concerted and focused effort to educate young people about the risks of unprotected sex."

The HPA recommended increased safer sex messages to the general public and reducing waiting times at clinics so people were diagnosed and treated for STIs faster. A department of health spokesman said health promotion is crucial to reduce the spread of HIV because there is yet no cure for Aids or vaccine against HIV. He said: "The government has made a long-term commitment through its national strategy for sexual health and HIV to improve sexual health and modernise services. HIV prevention and health promotion is a key element of this strategy. "

Testing for HIV is now offered to all first time attendees at GUM clinics on screening for sexually transmitted infections (STIs) and to all pregnant women. But he added: "The fact that the number of newly diagnosed cases of HIV have increased by 20% between 2002 and 2003 is truly shocking."

Tim Yeo, shadow health and education secretary, said: "It is time that the government listens to Conservative demands for a national service framework for sexual health and STIs. It will then be better able to set national standards and identify key interventions and ensure more is done to tackle the burgeoning public health crisis."