Smoke levels in Scottish prisons fell by more than 80% in the week after smoking was banned, research has found.

Despite fears prisoners may have stockpiled cigarettes before the ban on smoking in cells, scientists said the concentration of second-hand smoke was "drastically reduced".

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The study by researchers at the University of Stirling found that the quality of air inside Scotland's 15 jails was greatly improved by the ban after its introduction in November 2018, with smoke particles in the air down by 81% on average.

Dr Sean Semple explained how scientists collected second-hand smoke measurements from across the prison estate in the week that the smoking ban was introduced and compared them to measurements taken in 2016.

Dr Semple said: "We collected more than 110,000 minutes of second-hand smoke measurements from across the prison estate in the week that the smoking ban was introduced - and we compared these readings with measurements taken as part of the TIPS research in 2016.

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"Our study shows improvements in the levels of second-hand smoke in every prison in Scotland, with an average fall of 81%. This is similar to the scale of change observed when pubs became smoke-free in 2006 - and the concentrations of fine particles in prison air has now reduced to levels similar to those measured in outdoor air in Scotland.

"This research confirms that exposure to second-hand smoke has been drastically reduced and, ultimately, this will have a positive impact on the health of prison staff and prisoners."

Since 2006, smoking has been banned in most enclosed public spaces in Scotland but prisoners were still permitted to smoke in their cells as long as their doors were closed until the ban came into force.

A Scottish Prison Service spokesman said "All Scottish prisons went smoke-free on November 30 2018, and there have been no significant incidents as a result.

"This amazing achievement is a testament to the contribution made by all of our staff, especially those on the front line, and the cooperation of those in our care.

"Having data from the Tobacco in Prisons Study research helped in our planning and collaboration with the NHS, and has been key to ensuring people in our care were prepared for going smoke free and were offered help to quit in advance, similar to the support people in the community can access through their local pharmacy or GP."

Debbie Sigerson, organisational lead for tobacco in NHS Health Scotland, said: "Smoking rates in prisons were much higher than they are outside. It was anticipated that creating a smoke-free environment in prison would contribute to addressing this health inequality, and that the health of people who live and work there would be improved.

"We are delighted that the results from this study, early on in the implementation of smoke-free prisons, shows that one factor that impacts on that harm - exposure to second-hand smoke - has significantly reduced.

"Everyone has a right to live in a smoke-free Scotland and today's results show that we are one step further along the way to getting there."