The Family Planning Association is launching a new guide to help parents who blush at the thought of bringing up the subject of sex education.

'Talking to your child about sex' will be freely available in all Tesco pharmacies throughout August.

FPA chief executive Anne Weyman said research showed children felt their sex education was either too little, too late or too biological and that they prefer to talk to their parents about sex and relationships rather than to their teachers.

This is despite the fact that parents are not very likely to bring up the subject, especially with boys.

"Talking about sex can make parents very uncomfortable, often because of their own lack of sex education when young," said Ms Weyman.

The FPA is beginning a three-year strategy for supporting parents and carers in educating their children about sex.

It says more than one in 10 girls start their periods without knowing anything about them beforehand.

Sexual Health Week

The booklet is launched just before this year's Sexual Health Week, which starts on Monday.

The week is supported by public health minister Tessa Jowell. She said: "Openness in families about sex and relationships is a key factor in tackling teenage pregnancies.

"Research confirms that teenage births are more common among those who grew up in families where discussion about sex was difficult or did not take place. It is vital that we address this."

Britain has the highest rate of teenage pregnancies in Europe and the number of teen pregnancies and abortions continues to rise.