Volkswagen Group has said it has found CO2 emissions level "irregularities" that could affect 800,000 vehicles.

VW said that during its review of all its processes and workflows in connection with diesel engines, it found that CO2 levels and fuel consumption figures for some models were set too low during the certification process.

The latest revelation is a further blow to VW following the continued scandal surrounding NOx emissions on its vehicles. If CO2 and MPG emissions are clarified to be incorrect, it will have huge implications in the fleet market where company car taxation is set through CO2 levels. Consumers may also make a case for claiming compensation.

At this point, it’s unclear if any UK vehicles are affected. VW estimates the findings may cost the company upwards of £1.4 billion.

However, a spokesman for VW has told Automotive News Europe that fuel efficiency deviations are incorrect by a margin between 10% to 15%. He also said models affected are in Europe and include VW, Seat and Skoda models that use 1.4-litre, 1.6-litre and 2.0-litre diesels built in 2012 and later.

He said models identified that could be affected so far include VW Golf, Polo, Passat, Audi A1 and A3, Seat Ibiza and Skoda Octavia models. VW's 1.4-litre ACT petrol engine is also affected.

In a statement VW said: “The board of management of Volkswagen AG will immediately start a dialog with the responsible type approval agencies regarding the consequences of these findings.

“This should lead to a reliable assessment of the legal, and the subsequent economic consequences of this not yet fully explained issue.”

Matthias Müller, Volkswagen chief executive, said: “From the very start I have pushed hard for the relentless and comprehensive clarification of events.

“We will stop at nothing and nobody. This is a painful process, but it is our only alternative. For us, the only thing that counts is the truth.

“That is the basis for the fundamental realignment that Volkswagen needs.

“The board of management of Volkswagen AG deeply regrets this situation and wishes to underscore its determination to systematically continue along the present path of clarification and transparency.”

VW said it would do everything in its power to clarify events and ensure the correct CO2 classifications are given to the vehicles affected, which have not yet been revealed.

The company said a reliable assessment of the scale of these irregularities is not yet possible.