Charity Unicef has warned that Britain now has the highest number of new HIV infections in western Europe, with gay and bisexual men and black Africans most at risk.

In 2007, there were more than 7,700 new HIV diagnoses in the UK and the organisation has also said infection rates in young people are rising, with ten per cent of new infections occurring in those aged between 16 and 24.

The second highest figure for new infections was in France, with 4,075. Germany, which has ten million more people than Britain, had 2,752 new cases.

Four in ten of those diagnosed with the disease were men who have sex with men.

The latest figure is nearly twice as high as in 2000. It is estimated that there are around 77,400 people in the UK who living with HIV, although more than a quarter are thought to be unaware they are infected.

Unicef UK deputy executive director Anita Tiessen said that although immigrants from sub-Sarahan Africa were also one of the worst-affected groups, there was a “behaviour issue” leading to higher rates of infection.

She told Metro.co.uk: “It’s not simply a case of people coming here with HIV – there’s a behaviour issue.

“One of the ways you get sexually transmitted diseases is through unprotected sex. Safe sex will protect you from all sorts of diseases, including HIV.”

Deborah Jack, chief executive of the National AIDS Trust, said: “One in 20 gay and bisexual men are infected with HIV. Among black Africans that figure is one in 27. In the UK people are most commonly diagnosed in their 30s.

“We must educate our young people as behaviours learnt at a young age stay with people. Comprehensive sex and relationships education in schools must, for example, include education about same-sex relationships.

“General initiatives that focus on ‘youth’ are important for the epidemic internationally but risk overlooking the most affected groups in the UK. In the UK our efforts need to continue to focus on HIV prevention among the key groups affected – which remain gay men (including young gay men) and black Africans.”

A spokesperson from the Department of Health said: “HIV prevention remains a priority for us and that is why we continue to provide funding for the Terrence Higgins Trust and for the African HIV Policy Network for work with the groups most at risk of HIV in the UK – gay men and African communities.”