Nearly 700-thousand car drivers in Greater London could be liable to pay the ULEZ charge with the zone expands later this year.
Outer London currently has the lowest portion of compliant vehicles according to DVLA data.
The total figure that will have to pay the fee is likely to be higher when people travelling from bordering areas are counted.
Last month, Buckinghamshire Council called for the planned extension of the Ultra Low Emission Zone (ULEZ) to be scrapped and had written to the mayor of London.