Vehicles emitting more than 225g/km — or powered by an engine bigger than a 3.0-litre — and first registered on or after 1 March this year will be the ones initially affected. They'll be caught in the net from 27 October onwards.

Double cabs fitted with a 3.0-litre-plus engine, but registered before 1 March, won't be hit until 11 January 2010.

Examples of double cabs that will be clobbered by the £25 tax includes Ford's Ranger Thunder 156hp 3.0-litre automatic, with a 244 g/km emission figure. Also falling within the net are Nissan's Navara double cab (264g/km for the manual and 276g/km for the auto) and Mitsubishi's L200 (manual 228g/km, auto 252g/km).

Examples of vehicles that won't be hammered include Toyota's Hilux HL3 Double Cab 120hp 2.5-litre manual. It produces just 219g/km.

There's bad news too for people who have opted to run light commercials of between 1.205 tonnes unladen weight and 3.5 tonnes gross weight powered by liquefied petroleum gas or compressed natural gas, and whose vans are listed on the PowerShift or CleanUp registers.

Come 27 October 2009 they'll lose their 100 per cent congestion charge exemption. The only crumb of comfort is that they will be able to register with Transport for London and pay the discounted £6 a day charge to be levied on people who run vans that meet the upcoming Euro 5 exhaust emission legislation.

Owners of light commercials that meet Euro 5 and gross at between 1.205 tonnes unladen and 3.5 tonnes gross will be allowed to pay the reduced £6 rate from 27 October onwards. The discounted rate will last until 1 January 2012.