Drivers of dirty diesel cars could be charged a variable fee based on the pollution they emit under proposals being considered by local authorities.

The “polluter pays” system involves installing a monitoring device in vehicles that tracks their movements and measures in real time the amount of toxic nitrogen oxides they produce.

Drivers could be charged a higher rate for taking routes near schools in pollution hotspots or for choosing to drive in city centres during periods of high air pollution.

Unlike the flat-rate £10 “toxicity charge” being introduced for pre-2005 cars this year by Sadiq Khan, the mayor of London, the system would penalise drivers who produced higher levels of pollution by failing to maintain their vehicles or by driving aggressively.

Those who tried to minimise their emissions by driving smoothly and ensuring that their pollution controls were fully working would be rewarded by being charged a lower rate.

Tantalum, the vehicle tracking equipment company developing the system, said that it was working with Capita, the operator of the London congestion charge, on a 1,000-vehicle trial of the system starting in September. The trial would involve vehicles in commercial fleets or owned by leasing companies.

Transport for London and Mr Khan’s officials have met Tantalum to discuss the system and the company said that it was also talking to other interested local authorities.

Edi Truell, the former pensions adviser to Boris Johnson when he was mayor of London, is the largest shareholder in Tantalum.

He said that Mr Khan’s toxicity charge and Westminster city council’s 50 per cent higher parking rate for all diesel cars were “blunt instruments” that did not take account of the amount of pollution that each car produced. He said that the variable charging “would reward people for maintaining their vehicles well and for driving sensibly and in an environmentally sensitive way. With blunt instruments, people may have to invest thousands of pounds in a new vehicle when they may in fact be driving their existing vehicle sensibly and maintaining it well, meaning it may not actually be a high polluter at all.”

Some cities, including Paris, Athens and Delhi, respond to smog episodes by banning older cars on alternate days depending on whether they had an odd or even numberplate.

Mr Truell said that Tantalum’s system would allow a much more targeted approach, with drivers alerted in advance about pollution hotspots and given the chance to avoid them and pay lower charges by switching routes.

Tantalum has already installed equipment in several hundred thousand vehicles to monitor fuel consumption and driver behaviour to help fleet operators reduce fuel bills. Mr Khan is expected to confirm on Friday that he will introduce the £10 toxicity charge in central London this year for cars and vans that do not meet Euro 4 emissions standards, typically those registered before 2005. This will be on top of the £11.50 congestion charge.

About a third of the 30 million licensed cars in Britain were registered before 2005. However, only a fraction enter central London. Mr Khan is expecting his £10 charge to apply to 10,000 vehicles a day. The charging area could be extended to the North and South Circular Roads by 2020.

The Department for Environment, Food and Rural Affairs is working on a plan, due to be published in April, which could include charges for older diesel cars entering city centres.

A spokeswoman for Mr Khan confirmed that talks had taken place with Tantalum. She said: “TfL are working closely with industry to ensure the most efficient advanced systems are deployed in all future plans.”

To see the original Press Release: http://www.thetimes.co.uk/article/drivers-face-variable-charges-based-on-emissions