Volkswagen (Eric Dufour/Bigstock.com)

With rumours circulating that VW's CEO Martin Winkerkorn will step down on Friday, the fallout from the German firm's use of 'defeat devices' in diesel emissions testing continues. The company's share value dived nearly 20 per cent on the news, but has rallied a little since.

The models affected were sold in the US, but there are growing concerns that VWs bought in the UK – and indeed across the world – could have been built with defeat software installed.

The US Environmental Protection Agency (EPA) has accused VW of using defeat software in its diesel engine management systems to give false readings in emissions tests. In normal driving conditions, the models involved are said to emit up to 40 times more pollutants than are permitted in the United States.

The models affected are:

 

  • 2009 VW Jetta, VW Jetta Sportswagen – test groups 9VWXV02.035N/9VWXV02.0U5N

 

 

  • 2010 VW Jetta, VW Jetta Sportswagen, VW Golf, Audi A3 – test group AVWXV02.OU5N

 

 

  • 2011 VW Jetta, VW Jetta Sportswagen, VW Golf, Audi A3 – test group BVWXV02OU5N

 

 

  • 2012 VW Jetta, VW Jetta Sportswagen, VW Golf, Audi A3, VW Beetle, VW Beetle Convertible – test group CVWXV02OU5N

 

 

  • 2012 – VW Passat – test group CVWXV02OU4S

 

 

  • 2013 - VW Jetta, VW Jetta Sportswagen, VW Golf, Audi A3, VW Beetle, VW Beetle Convertible – test group CVWXV02OU5N

 

 

  • 2013 – VW Passat – test group DVWXV02OU4S

 

 

  • 2014 - VW Jetta, VW Jetta Sportswagen, VW Golf, Audi A3, VW Beetle, VW Beetle Convertible – test group DVWXV02OU5N

 

 

  • 2014 - VW Passat – test group EVWXV02OU4S

 

 

  • 2015 VW Jetta, VW Jetta Sportswagen, VW Golf, Audi A3, VW Beetle, VW Beetle Convertible, VW Passat – test group FVGAV02.0VAL

 

 

Many commentators have been surprised at the extent of the deception, which affects many thousands of VW cars. The German auto giant also owns a number of other motor vehicle brands, including Audi, Bentley, Bugatti, Lamborghini, Porsche, SEAT, Škoda.

Audi and Škoda, for instance, both use VW engines.

Experts say so-called "dieselgate" could also manifest in Europe, where diesel emissions tests are more prone to abuse.

There are also questions over whether such practices have been used by non-VW Group firms.