A prison is electronically scanning all incoming mail to combat attempts to smuggle drugs in on cards, photographs and bogus legal letters.
The screening arrangements were introduced to cut off the flow of illegal substances via “impregnated” correspondence into HMP Ranby in Nottinghamshire.
Drugs and associated issues of debt and violence were the “primary threat” to the stability of the jail, according to an inspection report.
New psychoactive substances – synthetic drugs previously known as “legal highs” – were the “clear drugs of choice”, HM Inspectorate of Prisons found.
Noting that the establishment had put in place a robust approach to tackling the drug supply, the report said: “The primary route into the prison of NPS and other substances was through impregnated letters (including false legal correspondence), cards and photographs.
“All incoming mail was electronically scanned for drugs and we were satisfied that the robust restrictions that applied when a test was positive were proportionate.
“Restrictions had also been discussed at the prisoner council where staff made efforts to allay any concerns over cross-contamination.”
Psychoactive substances such as Spice have been identified as a major factor behind the safety crisis that has hit much of the prisons estate in England and Wales.
Last week, the acting Prisons and Probation Ombudsman warned that the problem was “completely out of control”.
Smuggling attempts involving mail coated with drugs have been flagged up at several prisons.
In response to the trend, inmates at a number of jails are only allowed photocopies of their post, including children’s drawings, to prevent paper soaked in NPS from getting in.
Early indications from prisons that have introduced the measure are understood to point to a “significant” reduction in the number of NPS-related incidents.
The report on HMP Ranby said that, while the screening of all mail was “proportionate”, it often delayed delivery by up to 48 hours.
Drug finds and positive tests at the prison had decreased over the previous year, and longer-term analysis showed a reduction since it was last inspected in 2015.
“Despite this, incidents involving NPS were common and we saw prisoners under the influence of NPS throughout the inspection,” the inspectorate said.
Overall, the assessment concluded there had been a clear improvement at the category C facility, which holds around 1,000 men.
Chief Inspector of Prisons Peter Clarke said: “HMP Ranby had proven to be a difficult prison to run and still had many problems to fix.
“The key priority remained undoubtedly the continuing battle against drugs, which undermined everything.
“But that was not the whole picture. In our view the prison had unquestionably improved.”
Ranby is one of 10 prisons earmarked for extra funding under a Government drive to improve safety.
Prisons Minister Rory Stewart has pledged to resign if there is no reduction in levels of drugs and violence at the selected jails.
Mr Stewart said: “It is early days but I am really pleased to see improvements particularly in violence and safety.
“HMP Ranby is a challenging prison and this is why we selected it to be part of our 10 prisons project.”
Michael Spurr, chief executive of Her Majesty’s Prison & Probation Service, said: “I’m pleased that the chief inspector has highlighted the improvements achieved at Ranby, which are a credit to the governor and his staff.
“There remains more to do and we are taking firm action to reduce drug use and violence – particularly through improved detection, searching and perimeter security.”