Wandsworth prison's X-ray scanner not used for 'legal reasons'
Inspectors questioned why the technology had been taken out of action at HMP Wandsworth after proving effective in identifying contraband.
HM Inspectorate of Prisons (HMIP) found illicit substances, particularly cannabis and new psychoactive substances, remained "too accessible" at the establishment in south-west London.
Existing technology was not being used effectively, the assessment found.
"For example, the X-ray scanner in reception was no longer used and the CCTV cameras in visits were not monitored as a result, we were told, of a lack of staff," it said.
The X-ray scanner had been used previously and was an effective way of identifying contraband, HMIP said.
Inspectors were also told that inmates preferred the scan, which was more dignified than strip-searching.
"However, the scanner had fallen into disuse; we were told this was for legal reasons but we remained unclear about the reasons, given that similar scanners were in use in other establishments," the report said.
A Ministry of Justice spokeswoman said: "Wandsworth took a very cautious approach to new enhanced EU regulations on body scanners.
"Their use continued as normal across other prisons with scanners and we have now advised Wandsworth how to use the scanners effectively and in line with the EU regulations."
The report on HMP Wandsworth, based on inspection visits in February and March, said that in the previous six months searches recovered 277 mobile phones, 65 weapons and 153 drug packages.
In other findings, the watchdog said Wandsworth remained the most overcrowded prison in England and Wales, with most of the 1,428 men being held at the time sharing a cell built for one.
Chief Inspector of Prisons Peter Clarke said: "In essence, there were too many prisoners, many with drug-related or mental health issues, and with not enough to do."
Calling for "cultural change", he noted that not all staff carried anti-ligature knives despite six self-inflicted deaths since the jail was last inspected in 2015, and described the response to cell call bells as "totally inadequate".
Overall, Mr Clarke said it was "quite clear that there was a very real determination on the part of many dedicated staff at Wandsworth to make positive progress at this well-known and important prison".
Michael Spurr, chief executive of Her Majesty's Prison & Probation Service, said Wandsworth had been provided with extra staff and resources, its capacity had been reduced to ease pressure and the prison was strengthening its approach to preventing self-harm and suicide.
Prisons minister Rory Stewart acknowledged it was a "disappointing" report.
He said the Government was putting an extra £16 million into improving facilities at 11 prisons, including Wandsworth.