DRIVERS of old diesel-powered cars are being urged to think about trading them in for a newer model as a potential scrappage scheme looms.

The suggestion comes while the Government decides whether to introduce the scheme which would incentivise owners to trade in their diesels for new cars which are more environmentally friendly.

A previous government encouraged motorists to exchange their vehicles for diesel ones as it was thought that the cars’ lower CO2 emissions would be less harmful for the environment.

But environmentalists and Mayor of London Sadiq Khan have recently raised concerns about diesel engines emitting a high quantity of other harmful gases, such as nitrogen dioxide.

Now the Government is preparing to introduce a so-called “toxin tax” which will make it more expensive for drivers of up to 10 million older diesel vehicles to drive into urban areas like the middle of London.

They are expected to be charged up to £20 a day.

Dominic Threlfall, the managing director of Swindon Suzuki and Hyundai dealership Pebley Beach, said now would be a good time for owners to make the trade to a new diesel model or a petrol car.

He said: “Residual values of diesel cars are fine at the moment but the minute a scrappage scheme is introduced, or cities start charging diesel drivers extra to be on the road, part-exchange values will start to fall.

“Whether you should trade in now or wait for a scrappage scheme to be introduced depends very much on what you’re driving.

“If you have an older diesel worth £5,000 or less, it might be worth looking to trade in now but if you’ve got a 20-year old diesel worth £100, and scrappage comes in at £1,000 like it did in 2008 it’s clearly worth holding on to.”

A spokesman for Honda stressed that their new diesel engines are more eco-friendly than their older ones.

He said: “The modern diesel engines deliver on average 20 per cent lower C02 emissions than petrol engines and, with the latest technology, deliver significantly reduced NO2 emissions.

“On average, compared to 2000, nitrogen oxides are down 64 per cent, particulates down 90 per cent.

“We still see a role for diesel in Europe, it accounts for a significant proportion of the market.”

The Honda factory in Swindon produces diesel engines and newly introduced 1.0 and 1.5-litre petrol engines.

The spokesman said by 2025 two thirds of its sales will feature some form of electric powertrains.

Prime Minister Theresa May has said a decision on any scrappage scheme would be taken when the Government publishes a new air quality plan.