Westminster City Council has received strong criticism after announcing it will run a trial of emissions-based charging for diesel cars parking within Marylebone.

As part of its drive to improve air quality, a pilot programme will be introduced by the council from 3 April.

The charge for pay-to-park bays during normal parking hours will be raised for diesel cars. This will apply to visitors into Marylebone, with resident permits remaining unchanged.

The surcharge will add 50% to the current rate of £4.90 per hour.

Councillor David Harvey, cabinet member for environment, sports and community, said: “Residents and visitors tell us all the time that air quality is a key concern in central London and we have consulted with our partners and local stakeholders on this practical step in improving our health and wellbeing.

“We have had a positive impact and reduced vehicle emissions through our anti-idling campaign days and by encouraging sustainable and active travel. Additional charges for diesel vehicles will mean people think twice about using highly polluting cars and invest in cleaner transport that will make a real difference in the quality of air we breathe and our environment.”

However, UKIP transport spokesman Jill Seymour has called on the Government to prevent councils from “demonising” drivers of diesel vehicles with massive rises in parking charges.

She said: “The Government needs to step in and nip this money-grabbing scheme in the bud, before it spreads like wild-fire across other parts of the country.

“It is totally wrong for the authorities to be demonising drivers of diesel cars, just a few years after they were actively encouraging the very same people to buy them.

“These drivers bought diesel cars in good faith, on the back of incentives which were promoted by the Government.

“Instead of trying to penalise them, they should be focusing their attention on removing the diesel trucks, buses and taxis, which create far more pollution in our towns and cities.”

RAC public affairs manager Nick Lyes said: “Adding a 50% parking price surcharge to diesel vehicles is unlikely to make any difference to London’s air quality and will simply be seen as another charge on motorists. Westminster’s approach is also arguably not evidence-based as the surcharge takes no account of how much a vehicle is used and therefore how much it is contributing to the air quality problem – which calls into question the council’s assertion that they are applying a ‘polluter pays’ approach to tackling the problem.

“Without question tough action needs to be taken to improve air quality – our concern is that this blanket approach that applies to all diesel cars, regardless of how polluting they are, is simply the wrong one. The problem needs to be looked at in its entirety with any measures fairly applied across all contributors to poor quality air, be they private or business motorists, private hire firms or bus operators.”