Professor Neil McKeganey, director of the Centre for Drug Misuse Research, in Glasgow, said a new approach needed to be taken to tackle the problem as efforts to prevent drugs being smuggled into prisons were failing.
Figures from the Scottish Public Health Observatory revealed that 38 per cent of prisoners had used illegal drugs while in prison in 2013, a decline of 10 per cent on the year before.
Prof McKeganey, who has carried out research on drug use in Scotland over the last 25 years, said: “The treatment within prisons for drug addiction is being fundamentally undermined by the scale of the drug problem within prisons.
“It also seemed to me that it was virtually impossible to stop drugs from getting into prisons. I think many governors can see that now.
“I felt that we really need to take a different approach to stop drug use in prison. We want to tackle it from the user side, rather than from the supply side.”
He called for a system where all prisoners would be tested regularly, with rewards in place for those who stayed clean and measures to tackle repeat offenders.
Prof McKeganey said: “We wouldn’t tolerate drug use in other public institutions, such as schools. We don’t want people to continue their addictions – which may have contributed to their crimes – while in prison. We also don’t want people to become addicts when they go to prison.
“If we had universal testing then all the prisoners would know there was no way of them using without being found out.”
Testing could also cost far less than the measures preventing drugs being smuggled in, as well as the prison-based drug treatment which is undermined by clandestine use, he argued.
Prof McKeganey is currently working on an evaluation of drug use in prisons in England and Wales but he said the ideas should be applied across the UK.
Drug testing is currently carried out in Scottish prisons when it is part of an inmate’s sentence, or when prison staff believe the individual might be under the influence of drugs, according to the Scottish Prison Service (SPS).
All prisons carry out testing during one month per year as part of a process called Addiction Prevalence Testing (APT), where prisoners leaving and arriving in custody are tested to assess the levels within the institution.
Conservative justice spokeswoman Margaret Mitchell MSP welcomed the idea.
She said: “It will have a cost to it of course, but there is a much greater cost to preserving the current approach which is failing miserably.”
Hugh Henry, Scottish Labour justice spokesman, said it could make a “vital contribution” but warned the effectiveness and scale of testing should be monitored.
He said: “The Scottish Prison Service needs to consider whether the current practice is helping to reduce drug taking and whether increased testing could reduce the unacceptable level of drug taking in prisons.
“We should never tolerate the illicit use of drugs by prisoners.”
There are “robust” measures in place to prevent drugs entering prisons, according to the SPS.
An SPS spokesperson said: “Recovery is the explicit aim of all services providing treatment and rehabilitation for prisoners with drug problems.
“A range of substance misuse treatment and support services are provided, by adopting a multi-disciplinary approach, since individual prisoners require different routes to recovery.”