John Stubbs, head of technical policy for the AA, said: 'The current testing can pick up a badly tuned engine, but it does not give the whole answer as to how an engine is performing. An engine could fail a test, but be perfectly fine out on the road. There may just be slight carbon deposits on the fuel injectors or the vehicle may not be warmed up thoroughly that causes a test fail.'
But he said a more accurate test would be a long way off: 'There is a lot of head-scratching going on at the moment. A truly accurate test would cost too much and be too expensive and the vehicle would have to be run over a very long time, which is not feasible.'
One fleet has reported that in-house checks using the same equipment as MoT centres has revealed that 50 of its fleet of 600 1.8 N and P-reg turbodiesel Rover 200 and 400 models have illegal emissions. But it is certain the problem lies with the cars and not the equipment. A Rover spokesman insisted the company had not heard any comments from fleet or private motorists of emissions problems with its vehicles. He added: 'We will work with the company to work out why they are having this problem.'