The most popular children in school are to be recruited as anti-drug “influencers” in a Government funded project.

Teenagers, who have been voted by their classmates as the most influential, will be trained to discourage their peers from taking illegal substances.

The “Frank Friends” scheme, which is funded by the Government-backed National Institute for Health Research, will be run across 48 schools in the West of England and South Wales from September and will involve 5,600 Year 9 students aged 13 to 14.

Students in the top 17.5 per cent of nominations as the most influential in school will be asked to become peer supporters.

They will undergo two days of training and then be expected to have conversations about the potential harms of drug use with their peers over a 10-week period.

Half the schools in the programme will continue with their usual timetable, with the aim of evaluating the effectiveness of a peer-led drugs prevention programme in schools.

The three-year study, which is the UK's biggest trial of a school-based drug prevention programme, will be run by researchers from Cardiff University.

Dr James White, of the Centre for Trials Research at Cardiff University, said: "There is limited evidence that drug prevention interventions are effective.