Nearly 400 Lambeth residents have been caught fiddling their benefits by new voice recognition technology.
The pilot project saved £450,000 in benefit fraud.
Lambeth Council phoned 2,000 residents and used Voice Risk Analysis, which picks up minute changes in the voice that show a person is lying.
Benefits staff then made further checks to see if claims need investigation.
638 took part, and of these 377 were caught lying and had their benefits stopped or decreased.
A further 261 discovered they were not getting their full entitlement and had their benefits boosted.
The project, run in partnership with the Department of Work and Pensions (DWP) and Capita, has proved so successful that there are now plans to extend it.
Divisional Director for Revenues and Benefits David Ashmore said: "Lambeth has a clear and tough policy of zero-tolerance of fraud. We have a strong and multi-facetted counter fraud strategy.
"This cutting edge technology is another weapon in our armoury."
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