Ed Balls is facing legal challenges from faith groups and individuals over his announcement of mandatory sex education lessons for pupils before they reach the age of consent.

Religious groups reacted with anger to the move by the Schools Secretary, which will make it compulsory for all pupils aged 15 will learn about relationships, sex and drugs over the course of a year. The age of consent in the UK is 16. The Muslim Council of Britain vowed to mount a challenge to the new laws that it says contravene the right for children to be taught according to their parents’ tradition.

Shahid Akmal, chairman of the Muslim Council of Britain’s education committee, said parents would be forced to break the law because of their beliefs. “It will cause difficulty,” he said. “I cannot condone people breaking the law, but it will be an individual decision and some parents will feel that it’s the only option open to them.”

Others said the move could lead to the situation in which Roman Catholic schools would have to show children how to use condoms while teaching that contraception is a sin.

Times Archive, 1914: The teaching of sex hygiene

Speaking of these subjects must tend to break down the children's natural modesty

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A spokeswoman for the Catholic Education Service for England and Wales (CESEW) was “disappointed” the Government had abolished the right of parents to opt out of sex education. The move followed a two-year review and consultation period on how to make personal, social, health and economic education (PSHE) lessons mandatory. Discussions included Vincent Nichols, the Archbishop of Westminster, and the Church of England.

The new legislation will also force faith schools to teach more than just the biology of reproduction and include lessons on contraception, homosexuality and civil partnerships.

At present, they need only to have a policy on sex education, which can be a simple statement that they do not teach it. But Mr Balls insisted that after consultation “all schools accept that they will teach all the elements \ but they can do so within the ethos of the school”.

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.”

Faith schools would not be allowed to refuse to teach contraception on the ground 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.”

A third of England’s 24,000 schools have some faith basis. Fears were raised that the decision to curtail the right of removal combined with the new statutory teaching on sex would lead many more parents to remove their children from lessons. Mr Akmal said he would urge the Government to rethink its decision. Mr Balls said the number who opt to exempt their children is a “very small minority”.

The Government has no recent figures on how many parents do so, but Ofsted estimated eight years ago that four in every 10,000 prevent their children learning about sex from teachers. Norman Wells, director of the Family Education Trust, said the regulations go against the “fundamental principle in UK education law that parents are responsible for the education of their children”.

He added: “The Government has no evidence that children who are withdrawn from sex education classes are at greater risk of teenage pregnancy or sexually transmitted infections and no evidence that imposing sex education on them regardless of their parents’ views will bring any positive benefit.”

The changes, in 2011, come after two years of ministerial discussions about how to make PSHE lessons statutory. Children will also learn about the dangers of drug abuse and “risky lifestyles” and how to manage finances.

Teachers’ leaders welcomed the move. A spokeswoman said the CESEW was “disappointed” that a blanket right of withdrawal from sex education had been scrapped, but added: “We are pleased 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.”

Lisa Power, policy head at Terrence Higgins Trust, said: “Young people have said they need more support around sex and relationships and the Government has recognised this.”

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