Nightclub revellers in Preston will be allowed to decide to take drugs after receiving purity test results Getty

Drug users in Preston will be allowed to take party drugs like cocaine and MDMA as long as they test their purity before under a new scheme backed by Lancashire Police. Walk-in booths will be introduced on Friday and Saturday nights in the city so clubbers can find out what their drugs are mixed with.

In the new year, stashes of class A drugs will be scanned by laser equipment and give potential users purity readings about 30 minutes later. They'll then be left to decide whether or not to take them with returned samples being destroyed.

The service will be run by charity the Loop, which conducted similar smaller scale walk-ins at music festivals and found about a fifth of those who tested drugs decided not to take them after receiving the results.

Fiona Measham, professor of criminology at Durham University and co-director of the Loop, admitted to the Sunday Times that the scheme might seem "quite radical" but said it was "focusing on harm reduction".

"If we look at the evidence of other countries which already have this drug testing, we've found they have much lower mortality rates in relation to drugs," Measham said. "In Switzerland, they've had no party drug deaths for the last seven years. In the UK, 57 people died last year from ecstasy."

Critics argue the approach will backfire and instead "normalise" drug use with professor Neil McKeganey, founder of the Centre for Substance Use Research at Glasgow University, saying authorities had given the "green light" for consumption.

"I am staggered this is being contemplated. The police are advocating a view which one would not unfairly describe as facilitating drug use. By implication, the green light has been given by the authorities to consumption. It's hard to see how this isn't an absolute breach of our current drugs laws."