Driving reform: Police reveal the limits of clever ideas to save public money It is an easy mistake to make, says the AA, ready as ever to make excuses for car drivers: "Modern diesels are so quiet it's easy to forget you're driving one." Still, the story is useful as a parable of perverse incentives. Not only that, we learn that putting diesel into a petrol-engined car does not cause any lasting damage, while doing it the other way round can require repairs costing £5,000. Especially as the refueller usually gets back behind the wheel and drives off, oblivious to the further damage being caused. Police forces have tried all kinds of devices to remind officers, from bright yellow fuel caps to "talking" ones. These do not seem to be effective. So, on this question, The Independent finds itself on the same side as the Taxpayers" Alliance. The only way to stop public servants getting their hydrocarbons mixed up is to make them pay for draining the tank and providing a back-up car. Anyone can make one mistake, but the second time the pump dunce should pay.