Whether its supervised seems to depend on the station.
The one we fillup the trucks at dont seem to bother and just let the driver get on with it. But a local one to me seem to have the attendent out even in the rain watching it. Not seen anyone watching at local Tesco.
It kindof makes a mockery when the driver is covered in hivis everything, with helmet and visor. Then attendent in normal clothes with umbrella standing behind them.
Water in diesel, coupd get pricy.