The Coventry University study found that black pupils often had sex for the first time at a much younger age than their Asian or white classmates.

One in four 12-17 year-olds in the group of 3,300 pupils was said to be "sexually active", with half of those admitting they did not use a condom.

The researchers have called for reforms to sex education in schools, much of which risked being "too little, too late" as children experiment at a younger age.

The findings come amid continuing concern over Britain's high rates of teenage pregnancy and an alarming rise in sexually transmitted diseases.

Katie Newby, from Coventry University's Health Services Research Centre, told the media: "Sex education may be more effective if tailored to the preferences of different pupils. Our evidence suggests that 'one size does not fit all'.

"Providing sex education that equips young people with the knowledge and skills to inform their choices is crucial in tackling this problem," she said.

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