It was the news that he had been dreading. As Angus Nicoll talked to his counterparts in the US, they told him figure after figure showed without any doubt that the nightmare scenario had become reality. The signs were there; the syphilis epidemics in New York, Dallas and San Francisco; the surveys that showed that people were becoming less careful about safe sex.

But now the scientists at the United States' Centres for Disease Control told Nicoll that the disease that has claimed 21 million lives globally was bouncing back.

For Nicoll, the British Government's top adviser on Aids and HIV, the virus that causes it, the implication was clear: far from becoming a thing of the past, a manageable disease that is readily controlled, HIV is also set to make a comeback in Britain.

'We knew that the studies of people's behaviour were bad, we knew that the syphilis epidemics were bad, but this was confirmation that it's back. They are very disturbing findings,' said Nicoll, who is director of the Centre for Communicable Disease Surveillance at the Government's Public Health Laboratory Service. For Nicoll, whose job is to monitor and track Aids and HIV in the UK, the US results meant one thing: 'We know from the last big upturn in the 1980s that it happened first in the US and then here. We've had the syphilis epidemic here. It's now possible HIV infection could rise here.'

The US scientists tracked 3,000 young bisexual and gay men in six US cities, including New York, Dallas and Seattle. They found that infection among young gay men was climbing as fast now as at the peak of the epidemic in the 1980s. Every year 4.4 per cent of gay men in their twenties are becoming infected with HIV, almost twice the infection rate in the 1990s. One third of gay and bisexual black men in the US are HIV positive. For white gay men, the rate of infection was 2.5 per cent, whereas for black gay Americans it is 15 per cent each year, a rate that is comparable with those of sub-Sarahan Africa, the worst affected region in the world.

After the disease was first discovered in 1981, there was a huge surge in infection among gay men. Public awareness campaigns followed, putting extreme promiscuity out of fashion.

The disease has claimed 12,000 lives in the UK and 450,000 in the US. But with the success of combination therapies, the death rate fell sharply. The number of deaths in the UK has fallen from a peak of more than 1,500 in 1994 to 245 last year. In the first three months of this year, just 30 people died.

The public alarm bells about the return of Aids and HIV in the UK started a few years ago when the number of cases diagnosed started climbing again. The number of diagnosed infections rose last year to 3,434, the highest level since the epidemic began. For the second year in a row, more heterosexuals were diagnosed than homo sexuals. But the rise in diagnosis is thought to be largely because more people - particularly heterosexuals - are coming forward to be tested.

With fewer people dying, there are more people who are HIV positive and sexually active, capable of spreading the disease. The total number of people diagnosed as HIV positive in the UK is projected to grow from 23,000 now to 29,000 in four years.

The real concern will come when the UK follows the US, and the rate of infection starts rising. Nicoll has conducted similar surveys to those in the US and they show that it has stopped falling and stayed at a far higher level than previously expected: each year 2 per cent of gay men are becoming infected. The number of new infections each year within the UK is thought to be about 100 among homosexuals and 800 among heterosexuals. Just as in the US, the infection rate is now far higher among blacks than whites, with many of the infections coming from people who had sex in Africa.

Will Nutland, head of gay men's health promotion at the Terrence Higgins Trust in London, said new ways were needed to tell the safe sex message: 'There's evidence to suggest that young gay men who haven't seen huge numbers of gay men dying and attended the funerals of their lovers and friends, and been through that crisis, aren't behaving in the same way as the generation before them.'