Making drivers in London pay to use polluting cars is a 'welcome' principle, Hertfordshire County Council has said.

Responding to a Transport for London (TfL) consultation, the council said an expanded Ultra Low Emission Zone (ULEZ) would help reduce pollution over the Greater London boundary into the home counties.

Despite giving a nod to the clean air benefits of an expanded ULEZ, Hertfordshire County Council said TfL could not have its "full support" as a full impact assessment had not been carried out.

The consultation response reads: "Whilst we welcome the principle of the ULEZ, the full impact on neighbouring authorities has not been assessed and so we are unable to give our support at this stage.

"The council welcomes proposals which contribute positively towards cleaner air, climate change and congestion impacts are challenges which do not cease at the Greater London boundary. The council recognises that these ambitions are in line with the council's own corporate ambition of creating a cleaner, greener, healthier county."

London's ULEZ is currently in the area between the A406 North Circular and A205 South Circular roads.

Under the current rules, drivers in this area have to pay a £12.59 daily fee if their petrol car, van or minibus does not meet the Euro 5 engine standard, or if their diesel car, van or minibus does not meet the Euro 6 standard.

Motorcycle and moped riders whose vehicles do not meet Euro 3 engine standards must also pay a charge. A vehicle checker for motorists who might need to pay the fee is on the TfL website.

The expanded ULEZ would mean these rules would apply across 96 per cent of Greater London - the area currently covered by the Low Emission Zone for goods vehicles.

The county council response adds: "The county council considers there is a need to lobby for financial assistance or a tax rebate at a national level, as affordability will be a major issue for small businesses and individuals who will need to upgrade their vehicles to meet the standards in the shortest time possible.

"Any financial assistance should be targeted at renewal of fleet vehicles to meet required standards and incentives to engage modal shift to public and active transport modes."

The northern edge of the ULEZ would meet Hertfordshire's borders with Hillingdon, Harrow, Barnet and Enfield. Barnet and Harefield hospitals would fall in the zone, as well as High Barnet and Stanmore London Underground stations.

The Hertfordshire and West Essex NHS Integrated Care Board was not asked to respond to the consultation.