Barlinnie prison looms over the east end of Glasgow. The last remaining of the city's nine 19th century prisons, it is as famous a building among Glaswegians as anything designed by Charles Rennie Mackintosh.

But this jail, like almost every other in Scotland, is full. And though the chronic overcrowding has been roundly condemned by prison inspectors, the number of people being sent to Barlinnie is rising.