Prisoners were put on lockdown at a Scottish jail after a crackdown on mail.
Around 60 cons held in the protection wing at Kilmarnock HMP kicked off after mail was withheld due to a suspicion that drugs were being smuggled in by criminal gangs.
An insider said toilet and washing facilities were torn from walls and thrown at staff, who had been ordered to don riot gear to deal with the protest.
It is believed the latest outbreak of violence on Saturday evening led to several suspected ringleaders being shipped out to other Scottish prisons.
Prisoners are said to have been locked in their cells and the prison was hoping to return to normal during the course of Sunday evening.
A source said: “The tension grew after mail was held back, which was a result of information that suggested drugs were being sent in. It is possible part of the reason for the problem was the fact the drugs supply was cut off.
“There are various ways of criminals using the mail for drug running, including soaking paper in drugs in liquid form.
“The disturbance became serious enough for officers to deploy riot gear and back-up officers who were off-duty were drafted in to help put a lid on the trouble.
“Prisoners who were thought to be ringleaders were taken out and put in other jails.”
A report presented by Police Scotland to East Ayrshire councillors in June said there has been a “stark rise in serious assaults at HMP Bowhouse.”
It states: “We have been actively engaging with staff there to address this issue.”
Bowhouse and mostly holds criminals sentenced at Kilmarnock and Ayr sheriff courts.
HMP Kilmarnock was opened in 1999 and has a capacity of 692. It is privately run by private firm Serco on behalf of the Scottish Prison Service, the first of its kind in Scotland.
In 2005 the BBC program Panorama uncovered several failings in the operational running of the prison. It holds short-term, long-term and remand male adults.
Some of Scotland’s most notorious criminals have been held there, including gangster Robert Pickett, a senior member of the Lyons crime family,
Imran “Baldy” Shahid, who murdered innocent schoolboy Kriss Donald in 2004, was attacked in the prison’s gym after a feud and was lucky to escape with his life.
The Record contacted HMP Kilmarnock for a statement.
