Not one car on sale in Britain qualifies for Gordon Brown’s new zero-rated road tax band. In an embarrassing gaffe, government officials admitted they could think of no cars that produced less than 100g/km of carbon dioxide, the threshold for the tax exemption.

Brown announced in Wednesday’s budget that some cars would escape road tax altogether as a balancing gesture for higher rates of tax for higher emission vehicles.

But the vehicles officials believed would fall into the new tax-free band A are either no longer on sale (Honda Insight, ThinkCity car); are only sold abroad (Smart Fortwo diesel, Ligier Ambra); or are classed as “quadracycles” — basically four-wheeled motorbikes — which in any case are not taxed according to CO2 emissions and will continue to pay road tax based on engine size (Microcar MC1, Aixam A751). The one quadracycle that is road-tax free is the Reva G-Wiz, but this is because it is registered as a zero-emissions electric vehicle.

Widely misreported as a tax on “gas guzzling 4x4s”, the new top rate band G of duty will hit mainly people carriers, saloons and hatchbacks.

Among popular family cars that fall into band G and will pay £210 a year (£215 for diesels) are the Renault Espace, Toyota Previa and Ford Galaxy — Tony Blair’s family car of choice — the Citroën C5, Vauxhall Vectra, Mazda6, Honda Accord Tourer, Volvo S80 and some petrol-engined Ford Mondeos. The higher tax band takes no account of whether a vehicle is two or four-wheel drive; indeed, seven of the 10 top-selling 4x4s do not fall into the category, including most versions of the Land Rover Freelander, Honda CR-V, Nissan X-Trail and BMW X3.

Almost a quarter of new car customers will pay more road tax if they buy types of car similar to those sold last year. Of those, 8% will be in band G with CO2 emissions over 225g/km. “When Gordon Brown said just 1% of cars would be in band G it was an imaginative use of words,” said a spokesman for the Society of Motor Manufacturers and Traders.