Many British drivers like to tweak their vehicles but road safety experts say that by making three particular modifications motorists are breaking the law and risking lives.
Removing diesel filters, installing xenon headlights and chipping vehicle electronic control units all make vehicles illegal and can be dangerous. But few owners who do any or all of these end up being prosecuted, according to the Institute of Advanced Motorists (IAM).
Not only is it against the law to remove diesel particulate filters, but as of the start of this year it can also cause an MOT failure, the IAM's head of technical policy, Tim Shallcross, said.
He said filters can get blocked and cause breakdowns, especially with stop-start town centre driving, so some garages offer to remove them. Without filters, vehicles emit more CO2 and pollutants so the garages are doing work that is harming people's health, the IAM suggested.
Mr Shallcross says it is not possible to remove the filters by accident as engine management computers have to be reprogrammed to do so. It is being done on purpose, but people are seldom prosecuted for it, he said.
Copyright Press Association 2014