"In a single act of unprotected sex with an infected partner, adolescent girls have a 1% chance of acquiring HIV, a 30% chance of getting genital herpes.

Britain is facing a major teen sex health crisis.

The increase in sexually transmitted infections (STIs) and high levels of teenage pregnancy in the UK are "disturbing" and there is "no doubt" alcohol and drugs enhance sexual activity, Independent Advisory Group (IAG) on Sexual Health and HIV said.

It said young people are exposed to conflicting messages, with "explicit or subliminal" advertising and coverage of "celebrity" behavior being prevalent, while other information is restricted.

"For example, there are restrictions on advertising condoms pre-watershed, and on showing a picture of a condom out of its wrapper. Our young people are therefore receiving distorted messages."

(Watershed is the time after which adult content is allowed to be aired on TV.)

The IAG report said young people engaging in risky sexual behavior are at greater risk of contracting an STI, becoming young parents, failing at school, building up longer-term physical and mental health problems and becoming addicted to alcohol and drugs.

A recent UNICEF report put the UK at the bottom of a table of 21 countries for children's well-being.

It found that more children in the UK have had sexual intercourse by the age of 15 than in any other country, more have been drunk twice or more times aged 11, 13 and 15 than in any other country, and they are the third-biggest users of cannabis.