The oil company found an average 48% pass rate after testing cars and commercial vehicles at eight venues from London to Newcastle over the last two months. The results appear to support Mobil's claims made earlier this year which predicted wholesale diesel MoT failures following the introduction of a tighter emissions test last September (Fleet News, February 23), but which were questioned by independent experts.

The Government is also planning to crack down on dirty diesels still further with the introduction of roadside testing at 14 sites nationwide under the new Environment Act. The proportion of vehicles failing the Mobil smoke test ranged from 62% in London to 43% in Newcastle.