HMP Wandsworth have stopped using an X-ray body scanner for “legal reasons” despite similar devices in place at other jails across the country.
Inspectors have questioned why the technology had been taken out of the prison after proving effective in identifying contraband.
HM Inspectorate of Prisons found illegal substances, particularly cannabis and new psychoactive substances are “too accessible” at the south-west London prison.
Their report has found that existing technology at the prison has not been used effectively with 277 mobile phones, 65 weapons and 153 drug packages found in six months of searches before February 2018.
“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.
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.
Last month the inspectorate highlighted encouraging early results from the use of body-scanning technology at another jail, HMP Belmarsh, saying it had led to the discovery of mobile phones, drugs and weapons which would not have been detected during a strip search.
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.”
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.
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.