It's a criminal offence to sell an unroadworthy vehicle,so Trading Standards MIGHT consider a prosecution:
http://www.wigan.gov....yMisdescribedCars.htm
If the purchaser suffers a financial loss because the vehicle was falsely described, he can demand compensation (e.g. by a refund of what he paid for the car) and, if it's not forthcoming, he can pursue the matter through the civil courts.
If anyone suffers injury through the actions of the vendor (e.g. by selling an unroadworthy car as 'roadworthy') that person can also seek compensation from the vendor (through the courts if necessary).
Chris