A diesel engine cannot run on petrol, which can cause damage to the pump. Petrol in a diesel engine will act as a solvent, thus reducing lubrication and damaging the pump.
When the pump is damaged, metal particles remain in the fuel posing further issues to the rest of the fuel system. Some fuel systems can be damaged with the components in petrol. When petrol goes deeper into the system, it becomes more expensive to make repairs. Therefore, when petrol is accidentally filled in a diesel engine, the car should not be started. It is important to carry out a full drain, before starting the car.