Civil liberties campaigners revealed today that public bodies paid private investigators more than £3.9 million in the last two years to carry out surveillance work - including snooping on their own staff.
Big Brother Watch (BBW) said a total of 29 organisations paid private firms to undertake surveillance using powers under the Regulation of Investigatory Powers Act (Ripa) in the years 2010/11 and 2011/12.
The organisations include 27 councils, one public authority and one government department - the Department for Transport.
The Freedom of Information statistics revealed that four local authorities - Caerphilly, Dudley, Leicestershire and York - used private investigators to spy on their own employees.
But 14 organisations - 10 councils and four public authorities - paid private firms to undertake surveillance that was not covered by Ripa, commissioning potentially illegal activity.
The campaign group's director Nick Pickles said the revelations proved that surveillance laws were "not fit for purpose."
He said: "The government has acted to control surveillance by local councils but this research shows more than ever before public bodies are using private detectives to do their snooping.
"The law is at breaking point and public bodies shouldn't be able to dodge the legal checks on them by using private investigators."
BBW has recommended urgent reform of Ripa to protect against unauthorised surveillance by third parties.
Communities Secretary Eric Pickles said the government has clamped down on the overuse and abuse of surveillance powers by town halls and added it is "totally unacceptable" if councils were trying to sidestep important new checks.
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