A decision to drop plans for compulsory sex education in schools is a "betrayal" of young people, charity workers said today.
Schools Secretary Ed Balls blamed Conservative shadow Michael Gove for the loss of the proposals.
In a letter, he said: "There is now widespread agreement that statutory PSHE (Personal, Social, Health, and Economic Education) is essential to prepare young people for adult life, and our reforms would ensure that by reducing the age of parental opt-out to 15, all children receive at least one year of compulsory sex and relationship education (SRE).
"This is a very significant setback, which will deny many young people proper and balanced sex and relationships education."
The plan would have seen children learning about relationships from the age of five, but parents had the right to opt-out until they were 15.
Lisa Power, policy director of the Terrence Higgins Trust, said: "It's a disgraceful betrayal of the next generation. There's been very widespread agreement that young people need better sex and relationships education.
"The Government does not have an excuse that they did not know the date that the election was coming.
"It's been quite a long and hard struggle, so to chuck out the Bill for Lord Mandelson's Digital Bill is a bit rich."
She said that, without the reform, there would be a postcode lottery where some children would be left in ignorance.
Ms Power went on: "We will see the impact on young people who haven't had decent sex and relationships education. The girl who gets pregnant because the only education she got was in the playground, the people who use the word 'gay' as an insult.
"This isn't just about sex - it's about relationships, it's about bullying, it's about a whole raft of things."
What remains of the Children Schools and Families Bill is due to be considered by the House of Lords today.
Simon Blake, national director of sexual health charity Brook, said: "We are extremely disappointed that young people could be let down yet again after Government had finally accepted the need to make sex and relationships education statutory.
"A broad consensus has now been established between children, young people, parents and professionals in support of statutory sex and relationships education. All politicians must listen to this majority.
"We've got the evidence about what works to reduce teenage pregnancy, but statutory sex and relationships education in schools is the missing bit of the jigsaw.
"This section of the Children, Schools and Families Bill cannot fall at the last hurdle. If it does, we will let down another generation of children and allow them to experience the shame, fear and embarrassment that we see at Brook clinics every day."
Julie Bentley, chief executive of the Family Planning Association, said: "We were on the verge of witnessing a historic breakthrough in the sexual health education of children and young people in England.
"The loss of SRE within the Bill will deal a bitter blow to our young people, who consistently tell us that they want and need good quality information and advice on sexual heath and relationships.
"It appears the Bill has been sabotaged at the eleventh hour, but parents, teachers and young people themselves are united in their belief that statutory SRE is sensible and necessary, not to mention a right that young people are entitled to.
"We urge politicians to rethink this course of action and fully assess the potential consequences of it."
Sarah Smart, chief executive of the PSHE (Personal, Social, Health and Economic Education) Association, said young people had a right not only to learn about sex but other issues such as managing their finances.
She said: "This appears to be a tragic betrayal of children.
"Politicians had made a commitment to education that promotes the safety, health and well-being of our nation's young people and I cannot believe that they intend to reverse it.
"(For) Whoever forms the next administration, personal safety, debt, unemployment, drug and alcohol misuse, obesity will continue to impose a cost on individuals and families and the nation as a whole."
Fergus Crow, from the National Children's Bureau, said: "At the time of this recession, we need to provide our children and young people with the support needed to become financially literate and set the foundations for a lifetime of careful and effective financial management.
"We hear first hand that children and young people want good quality PSHE education, which includes support on understanding 'money' and, now more than ever, we would be doing them an injustice if we didn't act by ensuring this Bill becomes law.
"This is a very serious issue that will impact on the future well-being of children for generations to come - policy-makers approach it lightly at their peril."
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