Motorists won't be forced to pay more in road tax if their vehicles are found to be fitted with illegal software used to cheat emissions tests, the Government has today confirmed.

The news comes after German car-maker Volkswagen admitted 11 million of its diesel vehicles worldwide, including 1.2 million in the UK, are fitted with the software.

This switches engines to a cleaner mode when they are undergoing official testing, to make them appear 'greener' than they actually are.

Concerns had been raised that road tax – officially known as Vehicle Excise Duty (VED) – might increase for those whose cars were fitted with this "defeat device" software. This was just one of many concerns for VW drivers, see our VW scandal Q&A for much more.

The Vehicle Certification Agency, the UK regulator, is now working with car manufacturers to ensure this issue is not industry-wide. As part of this work it will re-run laboratory tests where necessary and compare the results with cars' emissions in real-world situations.

It's not just VWs affected, as the company also makes Audi, Skoda and Seat cars, although the issue only affects diesel vehicles, not those with petrol engines.

Transport Secretary Patrick McLoughlin says: "Our priority is to protect the public and give them full confidence in diesel tests.

"The Government expects VW to support owners of these vehicles already purchased in the UK and we are playing our part by ensuring no-one will end up with higher tax costs as a result of this scandal.

"We are also starting our testing programme to get to the bottom of what the situation is for VW cars in the UK and understand the wider implications for other car types to give all consumers certainty.

"I have been pressing for action at an EU-level to improve emissions tests and will continue to do so. I have also called for a Europe-wide investigation into the use of ‘defeat devices’, in parallel to the work we are doing in the UK."

VW has suspended the sale of 4,000 vehicles in the UK, which contain engines that may be fitted with this software.