Parents are to be forced to allow their children to have sex education before the age of consent, the Government announced today. Under the new laws, when children reach 15 their parents will lose the right to withdraw them from sex education.

At present parents can remove their children from lessons about sex until they are 19.

The move forms part of new laws that will make sex education compulsory in primary and secondary schools from 2011. Faith schools will not be able to opt out of any part of the new curriculum, although they will be able to teach topics within the "ethos of their faith".

Ed Balls, the Schools Secretary, said: "Sex and relationship education is a very important element and we see it as crucial to our drive to reduce teenage pregnancy."

The move is in response to a year-long review of sex education which found that 40 per cent of pupils are dissatisfied with the quality of teaching provided by schools on the issue.

A survey of parents, commissioned by the Government, suggests that 40 per cent believe children should attend sex education lessons but almost a third (30 per cent) said that the right to opt out was important regardless of the child's age.

Under the new curriculum, pupils as young as 7 will learn about puberty and the facts of life and 5-year-olds will be taught about parts of the body, relationships and the effects of drugs on the body. When they reach secondary school, pupils will learn about contraception, HIV and Aids, pregnancy and different kinds of relationships - including same-sex unions and civil partnerships.

Schools will be allowed to teach the subject "in line with the context, values and ethos of the school". It means that children at some faith schools could be taught that their religion frowns on the use of contraceptives at the same time as learning about condoms.

Mr Balls said: "It is open to faith schools to teach what they believe, according to the tenets of their faith, that pupils should not have sexual relationships outside of marriage."

But faith schools would not be allowed to refuse to teach about contraception on the grounds that they do not believe in sex before marriage, he added.

"You can teach the promotion of marriage, you can teach that you shouldn't have sex outside of marriage - what you can't do is deny young people information about contraception outside of marriage."

The Catholic Education Service for England said it was disappointed that the "blanket right of withdrawal" had been scrapped.

It added: "We are pleased that the Government has recognised that the right of withdrawal in formative years is most critical and is therefore providing for the ability of parents to opt out up to the age of 15." Paul Tully, general secretary of the Society for the Protection of Unborn Children, said: "We condemn this exploitation of the state-controlled school system by the Government to deliver its anti-life policies to children, by-passing parental involvement.

"The Government is removing the right of parents to protect their children from the explicit promotion of abortion and sexual health interventions in the latter stages. This will be exploited to pressure more schools to deliver government-style sexual health interventions. In recent years, these have been characterised by obscene and lurid presentations.

"These are the classroom equivalent of 'advertorials', promoting sex and birth-control products. They send the message to children: 'Do whatever you like - just be sure to avoid or abort any pregnancy'." Gill Frances, chairman of the Independent Advisory Group on Teenage Pregnancy, welcomed the new legislation.

"We believe this is the biggest single step which can reduce teenage pregnancy rates," she said "Evidence shows sex and relationships education helps young people delay early sex and make healthy choices when they eventually do become sexually active."

Today's announcement follows a review led by Sir Alasdair MacDonald, headteacher of Morpeth School in Tower Hamlets, East London, into the best way to make PSHE compulsory.

The move to a statutory curriculum is part of a strategy for cutting Britain's high teenage pregnancy rate and steering youngsters away from drug and alcohol misuse.

Under current rules, schoolchildren must be taught the biological facts of reproduction, which usually happens in science classes. Every school must have a sex education policy, but there is no statutory requirement for teaching about relationships and the social and emotional side of sexual behaviour.