Danger here of assuming that the weak mixture signal is a complete error and the issue is low voltage possibly through a tired battery but more likely through bad connections. The cold and damp comment suggests the latter.
In the OPs place I wouldcheck the battery voltage with a meter - after a nice run in Italy its unlikely that the voltage would be low enough to cause this sort of issue but still eventually start the car. Maybe try out a new battery from the other family vehicle?
The danger is that a weak mixture can cause a hole in the piston leading to other nasties. But if its a typical issue with Roadsters, its more likely the result of a Morgan exhaust system putting the exhaust sensors in a different location to that the Ford ECU was programmed for.
