The capital’s transport authority is seeking to reduce the number of motorists who use such sites amid concerns that they charge more than the official rate for entering the zone.
In some instances site operators have also failed to register vehicles with TfL, incurring penalties for drivers who then enter the zone.
Last month the Advertising Standards Authority ruled one site was “misleading” and ordered the firm behind it to implement a number of changes.
Some drivers have found the unofficial sites through adverts placed on websites and search engines, including Google.
However after receiving “guidance” from TfL, Google has promised “smarter enforcement” of its advertising policies to eliminate any misleading adverts.
Google UK’s Head of Policy, Theo Bertram, said: “We have always had a strict set of policies which govern what types of ads appear on Google and when we are notified that an advertiser is breaching those policies, we move swiftly to take action.
“Thanks to the further guidance provided by TfL, it is now easier to ensure London’s motorists are protected from misleading sites.”
Garrett Emmerson, TfL’s Chief Operating Officer for Surface Transport, said drivers “should only ever use our official website to pay the Congestion Charge” and promised further action to “protect” the public from unofficial sites.
