Fewer than half of the UK vehicles caught up in the Volkswagen emissions scandal have been fixed.
Only around 470,000 of the 1.2 million vehicles needing a ''technical fix'' have been dealt with, Volkwagen's UK managing director Paul Willis has admitted.
He had promised every car would be completed by the end of last year. However the deadline has now been extended until the autumn, with no compensation being offered to British drivers.
Appearing before the House of Commons transport committee on Monday, Willis denied his firm had misled customers, insisting it is an 'ethical company'.
It comes almost 18 months after it emerged the manufacturer had distorted its emissions data on diesel cars.
The technical measures offered to British drivers are designed to alter software and modify an air sensor to make emissions readings more accurate, even as VW insists 'defeat devices' to provide inaccurate readings were used in the US only and not Britain, this should reassure customers in this country.
Willis said, however, there had been 'issues' in making the modifications needed.
The firm was accused on Monday by UK transport minister John Hayes of acting ''extremely badly''.
Hayes said, ''This kind of curious inability to recognise their own failure seems to me to be, frankly, little short of ridiculous.''
However Willis denied claims that the fitting of cars with 'defeat devices' to provide distorted readings for nitrogen oxide was a ''mess'' for his company.
He said, ''I am a proud employee of Volkswagen, I think Volkswagen is an ethical company, yes, indeed.''
In the US, Volkswagen has agreed a $15-billion settlement, but the company's UK boss repeatedly said the company in Europe did nothing wrong and ''misled nobody''.
During a combative session of the Transport select committee, he insisted there was ''no legal basis'' for compensation claims, adding, ''At no time were any vehicles sold to anyone in Europe based on nitrogen oxide levels.''
Of the 1.2 million UK vehicles affected by the crisis, there were 508,276 Volkswagen cars, 393,450 Audis, 131,569 Skodas, 79,838 VW commercial vehicles and 76,773 Seats.
Around 20,000 cars a week are being fixed by the company, Willis told MPs.
He added, ''We are very pleased with that level of technical fix. Our customers are telling us that they are satisfied with the level of technical fix and we have been talking to the Department for Transport and informing them of this progress.''