Ok. Got it back today. 1st Service and I'm £175 lighter!
They could not find a fault with the car.
The diagnostics showed no faults, they even drove the car with the equipment connected (they covered nearly 12 miles on the road test) and no fault found. Car was left with them overnight, but the cold start this morning gave no problems. Typical, it did start behaving itself just after I booked it in, so maybe a contaminate in the fuel or something?
If it's working, then I'm happy. But they have asked me to come straight back in if it starts mis-behaving again. I asked about a software update, and they said that my car is all up to date but they did mention they will be checking with Fiat Technical to see if they have been issues (I did mention that they should check out this forum!)
They did fix the squeaking passenger seat which was starting to drive me mad. And they cleaned it as well!
Pete