New sex education classes with the message “no means no” are to be aimed at pupils as young as primary school age, the British Government has announced.

The initiative will involve telling schools to ensure youngsters understand the need for sexual consent at an “early age” as part of a drive to cut violence against women and girls.

The move comes as a new report in the US suggests a growing number of American young people are delaying when they first have sex.

The British plan is to incorporate teaching around consent in to the national curriculum.

A review will now look at how that can be done in practice and at what age it should begin. The lessons could start in primary school with the message being reinforced as they grow up.

Campaigners warned last night such lessons could “frighten” very young children and it was for parents to discuss such topics with their children, not teachers.

Any lessons on consent are expected to be included within personal, social, health and economic education (PSHE), where current sex education teaching is based.

A strategy to combat violence against women and girls published last November first signalled ministers wanted to teach children about consent, and at an early stage.

The cross-Government document said: “Children can be exposed to violence from birth and, unless an alternative view is established, are likely to grow to accept that behaviour as normal.

“Setting out which attitudes and behaviours are acceptable and which are not therefore needs to begin early on in a child’s life and be reinforced over time.

“Helping children understand early on the meaning of consent in relation to sex and relationships will be important in helping them make that distinction in later life.”

The action plan, to be published by Theresa May, the Home Secretary, today, will say the Government is driving that forward but the Department for Education is still to draw up the details of how it should be delivered.

Margaret Morrissey, of the Parents Outloud campaign group, said: “If they are going to do this then they need to be absolutely clear that they are doing it with the support of the majority of parents.

“And the majority of parents say ‘we will teach our children, we are capable and we do not want our very young children frightened’.

“Why should we put teachers in the invidious position of having to educate very young children about a topic 80 to 90 per cent will not understand?”

Meanwhile, a new report from the US shows a marked increase in the number of teens and young adults who are refraining from sexual relationships.

The government survey, based on interviews of about 5,300 young people aged 15 to 24, shows the proportion in that age group who said they’d never had any kind of sex rose in the past decade from 22 percent to about 28 percent.

The new report provides at least indirect evidence that “many, many young people have been very receptive to the message of delaying sexual activity — there’s no doubt about it,” according to Bill Albert, of the National Campaign to Prevent Teen and Unplanned Pregnancy, a US advocacy group.

There are other surveys of sexual behaviour, but this is considered the largest and most reliable. “It’s the gold standard,” Albert said.

Health scientist Anjani Chandra of the Centres for Disease Control and Prevention described the decline in sex as small but significant.

Data over the years on intercourse among never-married adolescents shows a steady decline since 1988. That seems to be in sync with other CDC studies showing an overall drop in teen pregnancy.

That the trend began in the late 1980s seems to undermine the idea that abstinence-only sex education — heavily emphasised during the 2001-2009 presidency of George W. Bush — is the explanation, Albert said. But it is possible those messages contributed, he added.

The national study showed that 27 percent of young men and 29 percent of young women reported no sexual contact.