LET'S assume there's some clear Government thinking on diesels before the new carbon dioxide-based company car tax regime comes into effect in April 2002. It should be obvious to policy makers by then that there are five different categories of oil-burning cars, not just one labelled prime suspect, and that treating each differently might encourage more fleets to choose cleaner vehicles.

From what we understand of harmful diesel emissions such as PM10s - sooty particles - the least green come from normally-aspirated units that still turn up in the bargain basements of some manufacturers' price lists. The other links in the smoke chain in ascending order of efficiency are indirect injection turbodiesels, direct injection turbos, common rail/high pressure TDs and then common rail with a particulates trap - the latter to be introduced in the Peugeot 607. Recognition of five diesel bands should allow the Government to revise the benefit-in-kind tax supplement without losing face.

Drivers of diesels would still cop a 3% penalty (sorry, supplement) on top of the CO2 percentage BIK price band, idTDs 2%, diTDs 1%, HDi/PDs on par with petrol and gas burners, and trappers like the 607 awarded a -1% incentive. Meanwhile, Toyota has hopped up a step to join the fast-growing common rail diesel technology - 0% supplement on our wish list.

Its 110bhp D4-D direct injection engine is its first twin-cam four valves per cylinder diesel and it comes in with the Avensis at SR level in saloon only and with a ú17,600 on-the-road price tag, a ú1,030 premium over the petrol. The 'old' indirect 2.0-litre lives on for the time being in saloon, liftback and estate variants but at the lower S and GS trims. The 2.0 TD GS four-door costs ú15,935.