NEARLY one in 10 adults is risking pregnancy or catching a sexually transmitted disease (STD) by having unprotected sex, a survey to mark National Condom Week reveals.

Researchers say that 22% of 18 to 20-year-olds and up to 15% of 16 and 17-year-olds admit to having had sex with a new partner without protection despite the well-publicised dangers.

The proportion of 25 to 34-year-olds who have changed their sexual behaviour to combat the risk of HIV and other STDs has fallen from 39% to 32% this year.

Meanwhile, a Scottish sex advice charity claimed yesterday that more than 60% of boys aged 14 and 15 do not know where to get free condoms or confidential help.

Edinburgh-based Lothian Brook Advisory Centre (LBAC) says the figure is even higher among lower age groups and, with one in three under-16s now sexually active, has launched its own safe-sex campaign targeting its message at young boys.

LBAC general manager Hawys Kilday claimed young males often miss out on sex education at home and school and do not know where to turn for advice.

''Figures also show that most boys don't know if they have a special young people's clinic available locally,'' he said.

''This means there could be hundreds of local teenagers left in the dark about contraception who may be putting themselves and their partner at risk.

''If we want young men to protect themselves and their partners against the dangers of sexually transmitted infections and pregnancy, we have to make sure they know where they can access free condoms.''

The centre, which offers a free condom service itself, will be urging youngsters to attend confidential advice sessions run each week at its offices in the capital's Gilmore Place.

Researchers at the Public Health Laboratory Service say the new figures on unprotected sex are worrying, particularly in the face of evidence that the number of STD cases is rising.

New cases of gonorrhea seen at specialist clinics have risen by 20% and chlamydia by 11% in recent years.

Overall, cases of acute sexually transmitted infections rose by 7% between 1995 and 1996.

This week's campaign, being sponsored by Durex, will be marked with display stalls, roadshows, dance nights and promotions at schools, colleges and pharmacies to promote safer sex.

Durex brand manager Debbie Zadeh said: ''It is vital that the message reaches as many people as possible - especially young people who are more likely to put themselves and their partners at risk by having unprotected sex.''

The earliest condoms were used by Ancient Egyptian tribesmen around 1350BC, while cave paintings at Combarelles in the Dordogne area of France reveal that condoms were in use in Europe by the first century AD.

In the 1500s, Italian anatomist Gabrielle Fallopius conducted the first known trials of a prophylactic condom when he invented a linen condom which protected men from syphilis.

Two centuries later, condoms made of animal gut became popular, leading to the emergence of condom shops.

In the eighteenth century, the Bishop of Peterborough wrote a poem celebrating the role of the condom in liberating young women, a copy of which is lodged in the British Museum.

Japanese condoms from the 1800s were made of thin leather or from tortoiseshell and horn.

In 1843, the discovery of rubber vulcanisation led to the first mass-produced reliable and cheap condoms. Rubber was used until the 1930s, when it was replaced by liquid latex.

During the Second World War, Durex joined in the propaganda battle against Germany by dropping giant condoms over occupied France to frighten the Germans into thinking British men were better endowed than they were.

The first lubricated condoms emerged in 1957, but it was 1969 before the first anatomically shaped sheath appeared.

Condoms are now used by around 25% of adults, compared with the 21% who rely on the combined pill for contraception.