Fresh media reports from Germany have accused top executives in Volkswagen of knowing for over a year that some of its vehicles had cheated in emission tests.

In November the company revealed that some 800,000 cars sold mainly in Europe had understated carbon dioxide emission levels.

These vehicles are separate from the initial 11 million Volkswagen vehicles which were found to have been fitted with software to fool tests.

At the time it said that it only learned about these cars when investigating the wider emission scandal - but Germany's Bild am Sonntag says that this is untrue.

It reports that Martin Winterkorn, the then Volkswagen CEO who lost him job after news of the company's emission cheating broke, knew about the discrepancies in the cars emission readings by spring of this year at the latest.

The report alleges that he was personally involved in the decision to pull the VW Polo TDI BlueMotion as a result of the car's heavily understated carbon emissions - and overstated fuel efficiency. It's actual fuel consumption was 18% higher than its reported level.

A Volkswagen spokesperson said that the car was taken off the market due to poor sales.

"The offering of the Blue Motion TDI Polo was suspended in all markets due to subdued demand," the company said, adding, "We are currently testing all models built from 2012 for differences in CO2 levels from the listed values."

In 2012 Mr Winerkorn promised that fuel emissions would be 30% lower in 2015 than they had been in 2006. Bild am Sonntag says that the company resorted to cheating to reach these goals.

This runs counter to the narrative put forward by Volkswagen which has suggested that workers may have gone rogue and worked to fool tests without the company's leaders realising.