Big Brother snooping powers were used to spy on Merton residents 30 times since 2008, new figures have revealed.
The surveillance action was conducted under the controversial Regulation of Investigatory Powers Act (Ripa), which allowed Merton Council to make 20 prosecutions for minor offences between 2008 and 2011.
The investigations included two incidents of fly-tipping and three prosecutions linked to unfair trading.
Over the same period, Bromley recorded the highest number of Ripa investigations with 206 and Barnet the lowest, with one.
This year, the law was changed and council will now only be able to use Ripa powers with approval from a magistrate.
Councillor Mehboob Khan, chairman of the Local Government Association’s safer and stronger communities board, defended the use of Ripa.
He said: “People quite rightly expect councils to tackle rogue traders, loan sharks and benefit fraudsters operating in their area.
“These criminals have been caught and prosecuted using evidence gained from surveillance.
“Without these powers it would be much harder, and in some cases impossible, to bring offenders to justice.
“On average, a local authority will only use these powers less than 10 times per year and national statistics show that council requests for communications data make up only 0.3 per cent of all requests received.”
Pressure group Big Brother Watch claimed public bodies including the BBC and Ofsted were using controversial surveillance powers to prevent serious crimes.
It is calling for such authorities to publish data on how often and why they use the powers, ensuring judicial approval of all surveillance operations and for a root-and-branch review of Ripa.
Merton’s cabinet member for finance Councillor Mark Allison said: “Merton uses its powers within the rules to deal with serious problems such as fly-tipping and door step scams. I am not ashamed of our tough stance on dealing with criminality and anti-social behaviour and I am sure residents agree that is the right approach.”