New figures show that a record number of gay and bisexual men were diagnosed with HIV last year in Australia.

Around one in four gay men with casual partners had unprotected sex in the last six months, with a significant rise for gay men under 25.

The Kirby Institute at the University of New South Wales conducted the research.

“It’s very alarming what’s happening with HIV at the moment,” said David Wilson, from the institute. “We’ve had over 1,250 cases of HIV recorded, that’s those that have been diagnosed”.

He added: “There are about 25% of cases that are undiagnosed in Australia as well.”

John de Wit, director of the Centre for Social Research in Health, warned many gay Australians seemed in the dark about HIV. “The idea that young gay men think that they might be immune in terms of young people and health, that’s not a new story.

“So in terms of what’s the relevant message for them, in terms of condom use but also HIV testing, these are the sort of things that we’re working on now with our campaigns.”

He added: “It’s important that people test regularly, and that they use condoms as much as they can, and that they test for STIs – particularly HIV.”

In July, the UK’s Department of Health said it was “concerned” by rising HIV infections among gay and bisexual men living in London.