Many young people do not use contraception because they do not believe they will have "bad" sex involving infections or pregnancy, say researchers.

Teenagers do not believe such consequences are relevant to them, according to sex advice charity Brook.

They are also unlikely to seek advice about contraception and sex if they are under-age because of worries about confidentiality and the law.

In surveys of young people carried out for the charity by Southampton University and an advertising agency, teenagers said they regarded safe sex messages as "preached".

It was not directly relevant to them because they did not consider themselves at risk of sexually transmitted diseases or pregnancy.

However, 40% of those questioned admitted to failing to use contraception because they were under the influence of alcohol or drugs.

Age of consent

Young people were unlikely to seek advice before the legal age of consent at 16 - young women who first had sex before they were 16 were six times more likely than over 16s to say "fear of being too young" was the reason they had not sought information.

"Bad" or "unhappy" sex was something that other people had, they said.

But young people who sought information before they first had sex were eight times more likely to use contraception than those who did not get professional advice.

Of those who went to a sex advice centre, 70% had already had sex - most young women went because they had had unprotected sex, experienced contraceptive failure or wanted to change their contraception.

Emergency contraception was the reason for the visit in the case of 40% of young women.

Alison Hadley, national policy officer for Brook, said: "Young people, particularly under 16-year-olds, won't risk asking for advice unless they are reassured that services are confidential and non-judgemental."

She said that information to teenagers must be done in an imaginative and innovative way which encouraged them to seek help with relationships and contraception.

The charity aims to launch a campaign in teenage magazines later this year.