VW claims many of these faults could be down to poor maintenance, with some of the cars even missing their DPFs. None of the issues is related to the fix, VW asserts.

VW hopes to have the fixes completed to all 1.2m by the autumn. The German manufacturer says less than 1% of owners have so far reported problems after the fix, which translates to around 6000 customers.

Insight: Is it time to give up on the diesel engine?

In a statement, Volkswagen said: “Far fewer than 1% of UK customers who own affected Volkswagen Group vehicles that have received the technical measures have reported any issues.

“That means that more than 99% of customers are satisfied with the application of technical measures, which of course are carried out free of charge. We make it a priority to look at the vehicles of the very small proportion of customers who report any issues.”

The VDCF claims the number of complaints and cars affected by the fix is actually much greater and that VW has not kept a log of complaints. The VDCF has urged the government to consider prosecuting VW.

A class action case being built against Volkswagen is gathering data in a survey of owners in the UK claiming their cars have been affected by the diesel engine fix.

In an email sent to those seeking class action by one of the law firms, Harcus Sinclair UK, it was claimed that of the 7504 survey respondents who had had the fix carried out on their car, 3925 have subsequently experienced a problem with their vehicle. Of those, 2103 have experienced reduced fuel efficiency, 526 have had their car enter limphome mode, and 200 claim to have been told by a garage that their fault is related to the fix.

Volkswagen's response to our test

“Volkswagen was not provided with sufficient information concerning the testing criteria nor an explanation of how such a cycle is representative of real-world driving.

“Volkswagen also notes that comparative fuel consumption measurements must be carried out very meticulously with, among other things, due attention to cycle profile, duration, the type of test rig and settings (including aerodynamic resistances, coast down data and load adjustments), the system used for the measurement and the scatter of test numbers.

“To attain a level of consistency, one measurement is not sufficient and more measurements must be completed on an identical vehicle. Further, as Autocar is aware, in any standard comparative analysis, comprehensive vehicle preparation would always be critical to the reliability of the values.

“It should also be noted that the relevant approval authorities have approved the technical measures and that during the development of the technical measures, Volkswagen worked with care to ensure that fuel consumption figures in the homologation cycle and on the road remain the same when compared with the previous software. If increases in fuel consumption were detected during the development phase, the software was revised and retested.”