There are also several codes of practice for garages. Bosch introduced the first, while others launched similar schemes, including the Society of Motor Manufacturers and Traders with its Motor Codes initiative, and the Good Garage Scheme.

Out of the garages tested, 15 were not affiliated to any servicing code, while Bosch and the Good Garage Scheme had 15 garages each.

Meanwhile, 80% of garages in the Motor Codes scheme are franchised dealers, so in order to fairly compare franchises and independents, Which? looked at 17 garages in total – 15 franchises and two independents that are part of the scheme.

Garages affiliated to the Bosch Car Service scheme scored highest, fixing 64% of introduced faults. Motor Codes garages came second with 60% of faults fixed, but those affiliated to the Good Garage Scheme scored 39% - worse than the 43% achieved by independent (non-code) garages.

Chris Mason, Motor Codes director, said: “We acknowledge that there’s still a way to go to ensure lasting improvements are made.”