Volkswagen is being judged again for its sins of emission.

The stock markets have already given their verdict, with Volkswagen's shares having lost a third of their value, around £21 billion since a scandal around rigging of exhaust emission tests broke.

Now UK sales figures appear to be confirming the fall from grace of the car maker which was until recently the biggest global manufacturer, in terms of sales. New registrations of VW-branded cars fell 9.8 per cent last month, while other brands owned by the giant including Seat (32.2 per cent) and Skoda (3 per cent) also sank.

Revelations have continued to damage the firm's reputation since it was forced to admit in September to installing "defeat" devices to cheat emissions tests. Since then it has also admitted that 1.2m diesel cars in the UK are affected, 11m worldwide. Then came the further concession this week that "irregularities" in emissions and fuel efficiency could affect both diesel and petrol engines. Only 800,000 additional cars are thought to be affected by this latest development, but it extends the damaging headlines. The company has already set aside £4.8bn to allow for possible compensation claims and sacrificed its Chief Executive in response.

It is not clear how directly the scandal has affected new UK sales, as some other manufacturers have also seen declines, while sales of other VW-owned brands including Porsche and Audi rose.

But industry insiders believe it is having an impact and the damage could go a lot further. The punishment the company is suffering at the hands of UK consumers may be just the beginning and is an indication of the task likely to face VW.

It is not enough for the company's US CEO Michael Horn to admit "we screwed up" as he did in September. Rigging cars with software to help them cheat emissions tests was dishonest and an active deception, not some bad business call. Customers will be rightly wary about purchasing cars if they cannot trust what they are buying, whether their concern is directly about environmental performance, about the risks of being taxed more for vehicles they thought were greener than the reality, about being misled about fuel consumption, or simply about resale value.

The real problem for a global brand is that the hit it takes is likely to be global too, even if some of the concerns about emissions testing are eventually shown to be localised.

Some fear it could be too much for the company, with its unusual internal political structure, to survive in its current form. The set-up - which involves a twin board, and a strong dynastic element in the company's management - almost certainly contributed to some bad decisions being made.

Turning around this perception of bad faith will take time to achieve. The financial crisis which engulfed RBS was different in nature from the Volkswagen scandal, but executives at RBS currently rebuilding the bank's reputation after years of greed and mismanagement, could no doubt explain how long it takes to convince consumers that a firm can be trusted again.