Transport for London (TfL) has warned motorists about copycat congestion charge websites.

Motorists who use these unofficial sites find themselves having to pay as much as £6 extra than if they paid direct through the TfL website.

One such site, paylondoncongestions.com, has been the subject of an investigation by the Advertising Standards Agency (ASA) and was instructed to make it completely clear that it was in no way affiliated with TfL.

Upholding three complaints made against the copycat site, the ASA commented that consumers were likely to be lead to believe that this was an official method of paying the congestion charge.

Garrett Emmerson, TfL's chief operating officer for surface transport, said: "TfL will be taking steps to seek to ensure that unofficial websites and search engines who allow them to advertise are not misleading the public."

Paylondoncongestions.com states it charges a service fee for checking and processing applications. Adhering to the ASA ruling, its website has been amended to clarify its lack of affiliation to TfL and make consumers aware of its extra charges.