Criminalising young people involved in the drug trade does not work, a senior Tory backbencher has said.

The declaration comes after the number of 14- to 18-year-olds convicted for possession with intent to supply drugs in England and Wales rose by more than two-thirds in five years, new figures showed.

School exclusions for drugs and alcohol rose by 57% over the same period, an analysis of official figures from 2012-12 and 2016-17 found. NHS data showed there has been a 50% increase in 11- to 15-year-olds using illegal drugs between 2014 and 2016.

It comes as thousands of vulnerable children and adults are being trafficked from cities to towns and villages around the UK to sell hard drugs on behalf of organised crime groups as part of the illicit “county lines” trade.

The majority of prosecutions and convictions for possession with intent to supply drugs among those aged 18 and under largely involved class-A drugs such as heroin, crack cocaine, cocaine and MDMA, data for 2016-17 showed.

The report by Volteface, a thinktank specialising in drug policy, and Mentor UK, a drug education charity, said dealers typically target impoverished children and those with behavioural and developmental disorders, and those excluded from mainstream schooling. Mentor UK said that many vulnerable children were being criminalised and excluded from school when they should be treated as victims.

“Criminalising our young people not only doesn’t work but it sentences children to an extremely difficult path ahead, making their recovery and reintegration extremely difficult,” said Crispin Blunt, a Tory MP and co-chairman of the all-party parliamentary group for drug policy reform. “No one wants to see their child have their chances in life ruined at secondary-school age.

“The only way to rid society of the trail of misery brought on by the illegal drugs market is to implement a harm-reduction and evidence-based drugs policy,” he said. “The government’s move to include drugs education in its draft plans for [relationships, health and sex education] is a welcome step in this direction.”

Niamh Eastwood, the executive director of Release, a charity specialising in drugs and drug laws, said the Home Office’s argument that drug laws protect children was flawed.

“We constantly hear from politicians and police that young people are being exploited as part of the county lines narrative, and how they are victims of the drugs trade,” she said. “However, these figures suggest that young people are being targeted by law enforcement and criminalised.

“At the same time, drug use among young people continues to rise. This is yet another indictment of the failure of the UK’s drug policy and why we urgently need reform which diverts people – especially young people – away from the criminal justice system.”

Anne Longfield, the children’s commissioner for England, said the rise in the number of children excluded from school for drugs was very concerning.

“Children who are caught with drugs need the support of schools and parents, not to be instantly kicked out of school,” she said. “I want to see consistent policies around drug possession that keep children in school whenever possible. Excluding children just puts them at greater risk of becoming involved with gangs or exploitation and diminishes their life chances.”