Vehicle fuel tank with inlet for receiving a pump nozzle for diesel fuel

The vehicle fuel tank has a tubular slide (6) in the inlet which corresponds in diameter to the nozzle (3) of a diesel oil pump. This is biased towards the top of the inlet, so that it closes off the air outlet (5), but is pushed down to free it when the nozzle is inserted. If a petrol pump nozzle is inserted, it is too narrow to move the slide and it is impossible to fill the tank.