Vauxhall Vectra 2.8i V6 Turbo
Most casual road users wouldn't think a Vectra could do any substantial amount of damage to the environment but when you up the Vauxhall's power with a V6 Turbo you get both va-va-voom and global doom.
Its emission rating stands 25% above the average in its class and only grants the lucky driver 25mpg while bumping him or her into tax band G. It recently made its way into the 10 most fuel inefficient motors tested by WhatGreenCar?