Legalising cannabis could lead to an extra one million using the drug with 100,000 becoming addicted, according to a new study which warns of the dangers of “sucking young people into the mayhem”.

A report by the Centre for Social Justice (CSJ) linked cannabis use to mental health problems and found “a very real prospect” of more young people taking up the drug if it becomes legal.

New YouGov polling, cited in the report, revealed that nearly a quarter of 18-24 year olds who had never used cannabis before would “definitely or probably try it” if the law changed - equating to more than one million new cannabis users under the age of 25 alone.

According to WHO and NHS estimates, at least 10 per cent of this number would become addicted - 100,000 people, with the rate of addiction thought to be 10 per cent in adults but as high as 1 in 6 users under 25.