If you thought that the Volkswagen diesel emissions scandal couldn't get any worse, you were sadly mistaken. The company is now reporting that it has found "irregularities" in the carbon dioxide emissions levels of around 800,000 cars. That figure is just for Europe, too; the worldwide number of affected cars could be much higher.

The original VW scandal revolved around nitrous oxide (NOx) emissions. Nitrous oxides are a toxic pollutant produced by diesel engines. There are ways of reducing the amount of NOx produced, though, such as catalytic reduction with urea. The other method, as VW has shown us, is to cheat on the emissions testing. Cheating tends to be cheaper in the short term, but it's quite tricky in the long term if you get found out.

Now, however, VW is reporting that around 800,000 cars, mostly with 1.4-litre diesel engines, may have an issue with their carbon dioxide emissions as well. The two main cars affected are the VW Polo and Golf, but some cars from the Audi, Seat, and Skoda brands are also included. VW says that some 1.4-litre petrol engines may also be affected, but the company didn't provide any further details.

It seems that while VW was investigating the "defeat device" that intentionally and artificially reduced NOx emissions during official certification, it stumbled across some similar inconsistencies in CO2 testing. VW hasn't provided many details yet, but it sounds like the cars were producing significantly less CO2 during emissions certification testing than in real-world use. "During the course of internal investigations, unexplained inconsistencies were found when determining Type Approval CO2 levels,” a statement from VW said. “Based on present knowledge, around 800,000 vehicles from the Volkswagen Group are affected.”

While cheating on NOx emissions is one thing, these CO2 irregularities could be far more damaging for VW. CO2 emissions are generally quite closely tied to fuel consumption. If VW was cooking the books to show higher mileage and lower emissions than what you'd actually get in real-world use, it could be on the hook for some huge regulatory fines. The company says it has already set aside €2 billion (£1.4 billion or $2.16 billion) for the 800,000 cars that may have CO2 issues; that's about four times as much per vehicle than what VW set aside for the NOx defeat device issue.

Volkswagen has so far written off €6.5 billion ($7.05 billion) for the 11 million vehicles affected by the NOx emissions issue. If the CO2 issue turns out to involve more than 800,000 cars, then VW could be looking at a further write-off of tens of billions of euros. Unsurprisingly, VW's shares have tumbled about 10 percent since the company first announced the CO2 irregularities late last night.