The chancellor announced he would be introducing a new top tier of vehicle excise duty, or road tax, up from £165 to £210 a year.
In return, Mr Brown said he would be exempting the least polluting cars from tax altogether.
Meanwhile, up to five million motorists would see their car tax cut or frozen.
However, the AA says that the total number of cars that will pay no tax at all is just 400.
By contrast, the decision to introduce a new CO2 emission top tier, measured in grams per kilometre, of 225, itself up from 185, not only brings in high-performance sports cars and large 4x4 vehicles, but also many family cars.
Among the vehicles affected is one of Vauxhall’s five-door 2-litre Astra models, along with some Minis.
Unsurprisingly, the AA is unimpressed by the announcement.
It points out that the extra £45 in annual road tax is unlikely to influence buyers of a new Lamborghini, Ferrari or even a Porsche Cayenne.