Police in Leicester say they hope the introduction of plain-clothed officers onto the streets of Leicester will make people think twice before committing crime.
The scheme is codenamed Operation Rhesus.
It was used for the first time in the city centre at the weekend.
Officers say they intend it to become a regular part of policing on Friday and Saturday nights.
One of those in plain clothes, Pc Dave Piguiellen, said:
"What we're trying to build up, in the public, is the perception that there could be a police officer anywhere - they don't have to be in big yellow jackets.
"It's not always going to be effective because people may commit disorder offences and assault people when we're not there.
"But what we're trying to put in people's minds that there could be a police officer there, so try and behave yourselves even if you don't see a police officer immediately."