Nearly all cannabis on Britain's streets is now super-strength skunk that could be fuelling the rise in mental health problems, scientists have warned.

Researchers at King’s College London tested almost 1,000 police seizures from Kent, Derbyshire, Merseyside, Sussex and the capital in 2016 and found 94 per cent were of a dangerously high potency.

In 2005 just 51 per cent of cannabis sold on the street was sinsemilla, also known as skunk.

Dr Marta Di Forti, Medical Research Council Clinician Scientist at King’s College warned that the powerful drug placed Britain’s 2.1 million cannabis users at risk of schizophrenia, bipolar disorder, depression, psychosis, delusions and hallucinations.

‘The increase of high-potency cannabis on the streets poses a significant hazard to users’ mental health, and reduces their ability to choose more benign types,’ she said.

“It is of concern that 94 per cent of seized cannabis is now of skunk type as this potentially could increase the number of people using it and consequently the number of people experiencing harm.

“Regular users of high-potency cannabis carry the highest risk for psychotic disorders, compared to those who have never used cannabis.”