TESTS for drugs being taken by inmates at Greenock prison showed that nearly a third were positive.

Scottish Conservatives said that, of 17 Gateside prisoners tested for taking illegal substances, five proved to be positive — 29 per cent.

Three were for cannabis, one for opiates and one for methadone.

Scottish Conservative shadow justice secretary, Liam Kerr, said official statistics show 1,164 inmates in Scotland were caught either taking drugs or administering them to others last year, the equivalent of more than three a day and nearly double the 634 caught four years ago

The figures don’t include convicts who have taken drugs and managed to get away with it.

Mr Kerr said: “In recent years the Scottish Government has introduced measures such as signal jamming trials to reduce the illegal use of mobile phones inside.

“But no such progress has been made on drug-taking, with last year’s the highest number of incidents since 2008-09, when 1,257 were caught.

“Yet again, we see offenders continuing their criminality within prison walls, an environment which is supposed to be completely secure.

“For the second year running, more than three inmates are being caught using drugs every day, and these figures indicate it’s getting worse year after year.”

Mr Kerr said that detecting and recording incidents isn’t enough.

H said: “It’s crucial the Scottish Prison Service (SPS) cracks down on this problem and stops these substances slipping through the net.”

A spokeswoman for the SPS said a comprehensive range of robust security measures are in place to prevent the introduction of contraband into prisons.

She added: “Significant investment continues to be made in the development of new technology and staff training to detect, deter and reduce the availability and supply of illegal drugs.

“Anyone found in possession of contraband is reported to the appropriate authorities.”