According to Medway Autos in Rainham, Kent, (who were very helpful, by the way) the P2018 fault code neccesitated the replacement of a 'swirl valve' and is an acknowledged issue that Alfa are aware of.
That was three days ago. Today, with the low-fuel light having been on for half-an-hour or so, the same fault light came on again (not when driving, after having parked for an hour). Initially there was a lack of power as the engine stayed in nice, safe economy mode. Then having filled up with diesel, firstly the power returned, then starting it again, the fault light stayed off.
Could it be that the diesel injection system doesn't like the fact that the tank is almost empty and that the fuel pump may be struggling to draw fuel up at the required pressure for the initial start-up???
Anyone got any ideas?