A fuel filling system

The system comprises a diesel fuel filler orifice 12 on the vehicle for receiving diesel fuel from a diesel fuel supply nozzle. The diesel fuel filler orifice 12 is of non-circular cross-section and has a minimum internal dimension which is less than the external diameter of a traditional lead free fuel pump nozzle. A diesel fuel supply nozzle is also disclosed. This supply nozzle has a maximum external dimension greater than the internal diameter of a traditional leaded fuel filler orifice.