One of Britain's most popular small cars emits as much N02 emissions as a heavy duty lorry, new research has found.

The VW Polo was disgraced in the 2015 Dieselgate scandal and manufacturers pledged to slash its release of harmful gases after it was found to be routinely cheating on emissions testing.

Now, scientists at Leeds University's Institute for Transport Studies said the car is one of the worst polluters on Britain's roads after the research body was commissioned to carry out the study by Transport for London.

"The worst-performing car [in the tests] was a VW Polo with a 1.4-litre turbodiesel engine with NO2 emissions 13 times higher than EU regulations allow," said James Tate, who authored the study.

"Its emissions of 1.2 grams of NO2 per kilometre were the same as a fully laden diesel truck with a 13-litre engine that we also tested," he detailed.

The study, carried out alongside vehicle-testing firm Millbrook, involved 13 cars and four lorries – all with diesel engines.

After the acceleration, cruising and deceleration patterns were recorded around London at different times of the day, the cars replicated the driving patterns on rolling roads so emissions could be precisely measured.

"The key finding was that small diesel cars emitted far more pollution than larger cars and even lorries," said Tate.

Other high polluters included a Vauxhall Astra, Ford Focus and BMW 318d, according to the research.

By contrast, the bigger VW Passat was found to be one of the lowest-emitting diesel of the cars studied.

Researchers found that smaller cars lacked the space for the sophisticated equipment required to reduce emissions.

"This shows the emissions problem can be solved, but for cheaper cars the technology is too expensive and there may not be enough space to fit all the extra components," said Tate.

The revelation comes as 30 towns across the UK considered banning diesel cars from the roads.

A security personnel walks pasts Polo at German automaker Volkswagen plant in Chakan. Reuters