BBC Watchdog has joined forces with Auto Express to highlight technical issues experienced by “thousands” of Volkswagen customers following implementation of the dieselgate emissions ‘fix’.

Reporting on the findings of an investigation by UK law firm Harcus Sinclair the programme, screened last night, revealed that 5,052 of a sample of 9,500 Volkswagen owners reported reduced fuel efficiency or reduced power and acceleration following the work.

Some 14% of drivers claimed their cars had gone into 'limp mode' with one woman featured in the Watchdog programme claiming that her car was struck by a lorry as she tried to steer to safety after it lost power.

Watchdog’s investigation found that fixed cars’ Exhaust Gas Recirculation (EGR) valve was working harder than it should be.

Data gathered by Hypermiler.co.uk on behalf of Auto Express revealed that 87% of the 542 owners who had the emissions fix carried out experienced mechanical problems, of which 66.9% experienced issues with the EGR system.

Damon Parker, head of litigation at Harcus Sinclair, which is leading a class action lawsuit against the Volkswagen Group and has seen more than 35,000 owners in England and Wales have so far joined the lawsuit so far, said: "These results show that the fix intended to reduce NOx emissions may in fact have a detrimental impact on the car’s performance and running costs."

In a statement issued to Auto Express, Volkswagen defended its position, claiming that “there is no systemic problem” and that “the overwhelming majority of our customers have been fully satisfied”.

Volkswagen said that the relevant authorities have confirmed that the technical measures “have no adverse impact on the mpg figures, the CO2 emissions figures, engine output, maximum torque and noise of the affected vehicles”.