The UK boss of Volkswagen has defended the speed of the car firm's response to the diesel emissions scandal and apologised "sincerely and unreservedly" to customers.

More than 1,000 cars fitted with pollution test-cheating software were sold in the UK after it emerged that this country was also affected by the issue.

But Paul Willis said he halted sales within hours of confirming which particular models were affected and could not have acted any faster.

His comments came as the marque took out full page advertisements in newspapers, including The Herald. The company said it had broken the trust of its customers and added it would be contacting every customer affected directly to resolve the problems.

The German carmaker has admitted that 11 million of its vehicles worldwide are fitted with software which was used to cheat environmental tests in the US.

Close to 1.2 million vehicles are affected in the UK with recalls of cars due to start in the first quarter of next year for remedial work.

In a grilling by the Commons transport committee, Volkswagen UK managing director Mr Willis conceded there was "some risk" that a target of doing all the work by the end of next year would be missed.

Some 400,000 would need changes to their fuel injection systems as well as having the software removed, he said - though he was unable to give any technical explanation to the frustration of MPs.

Engineers were under orders to ensure that the fuel efficiency of the cars involved was not reduced as a result of the changes, he insisted.

Asked why cars continued being sold - more than 4,000 after the scandal first broke in the US according to committee chair Louise Ellman - Mr Willis said it was 1,079 after it became clear Europe was affected.

"I couldn't stop selling cars if I didn't know which cars were affected," he told MPs - saying he received those details on September 30, eight days after it emerged Europe was affected and two days after he told the Government sales would stop when they could.

"There were eight days between when we first knew it affected Europe until I stopped selling cars and the reason for that is the complexity of the number of cars involved.

"There are 60 different models, there are five different brands, there are three different engines and two different transmissions.

"I found the VIN numbers out precisely at 9am and at 1:30pm, once I had clarified it with the computer systems, I stopped selling the cars voluntarily."

He said the testing regime was "old fashioned and not fit for purpose" but that was no excuse for the actions of the firm.

"We mishandled the situation. That's why we need to fix the cars, that's why we need to get the customers in and need to put the cars right.

"We mishandled the situation without a shadow of a doubt."

He said an "independent wide-ranging investigation" had been established by Volkswagen in Germany but he did not know whether the deception over testing of VW diesel engines was the result of a high-level corporation decision or a few rogue software engineers acting without the knowledge of senior managers.

"I find it absolutely implausible that senior people in the company would have known of these issues with regard to the testing regime," he said.

Mr Willis said that sales and orders for VW vehicles were down "a little bit" since the scandal broke, but that the company's other brands were selling as would normally be expected.

Transport Secretary Patrick McLoughlin told the committee that VW "have behaved in an appalling way".

The devices being used to mask emissions had been outlawed as long ago as 1988, he said, adding: "It is fairly unbelievable to think that a company of the size and reputation of VW has been doing something like this and finding ways around regulations.

"I think they are going to suffer very substantial damage as a result of it and they deserve to, quite honestly.

"It draws questions we then have to ask about the overall testing of emissions and that's exactly what we are going to be doing."

The emissions scandal was sparked by US environmental regulators who found that VW had installed defeat device software which switched engines to a cleaner mode when they underwent official testing.

Once on the road the cars produced nitrogen oxide pollutants at up to 40 times the legal standard.

Mr McLoughlin said: "I don't think we should overall condemn the whole industry because one player has been caught doing something they shouldn't have been doing, which will cost them very dear.

"There is no doubt as to the cost that this is going to have for Volkswagen. It's not acceptable for a company of this size."

Mr McLoughlin indicated that he could take legal action against VW.