Media playback is unsupported on your device Media caption Jason Warriner, clinical director of the Terrence Higgins Trust explained some of the reasons for the rise

There has been a big increase in the number of people aged 50 and over catching HIV, latest figures show.

The over-50s infection rate in England, Wales and Northern Ireland more than doubled in under a decade - from 299 new cases in 2000 to 710 in 2007.

In 2008 there were 7,382 new diagnoses - 8% of these were in the over-50s, says the Health Protection Agency.

Experts say the figures are a stark reminder of the importance of practising safe sex, whatever your age.

Other sexually transmitted infections have shown a similar doubling in under a decade among the same age group, and have been rising at a faster rate than in the young.

Promiscuity

Ruth Smith, who led the HPA research, said: "We estimate that nearly half of older adults diagnosed between 2000 and 2007 were infected at age 50 or over. This highlights the importance of HIV testing - whatever your age.

This highlights the importance of HIV testing - whatever your age Ruth Smith, HPA scientist

"We must continually reinforce the safe sex message - using a condom with all new or casual partners is the surest way to ensure people do not become infected with a serious sexually transmitted infection such as HIV."

Worryingly, say the researchers, half were diagnosed late. The sooner HIV is diagnosed and treated the less likely it will be passed on and the better the treatment options become.

Dr Valerie Delpech, head of HIV surveillance at the HPA, said: "HIV remains a serious infection particularly when diagnosed late. The fact that we've seen an increase in the number of older adults getting diagnosed, and in particular getting diagnosed late, highlights the need for raised awareness in that age group."

Lisa Power, of the HIV charity the Terrence Higgins Trust, said their own research had found the over-50s were now the fastest growing group of people with HIV in the UK.

"This is partly because people are now living for longer with the condition, thanks to better treatment. Life expectancy with HIV has improved."

But she said there was a long way to go regarding support for this age group.

"Older people with HIV are living with high levels of uncertainty about their future health and social care and need substantially more support than their peers."

All of the findings were presented at the Aids 2010 conference in Vienna.