Well, just for completeness, here's an update:
Getting the bike back coincided with the council starting to salt the roads, so I only got the one 80 mile test ride in before Winter.
About a month ago, with little salt down and during an unusually mild March, I went out to enjoy the bike. Sadly my enjoyment was cut short by a large oil leak after 5 miles.
I found that the oil temperature sensor in the head was broken, I would guess overtightened by the dealer "mechanic" during the (unecessary) head replacement.
Having given up on the warranty by this stage, I ordered one and fitted it myself.
Another couple of rides went by, then on a ride out with a mate, the engine cut out suddenly. I checked the usual, fuel pump relays etc, but all seemed well, until I noticed no sloshing noises as I moved the bike. The tank was empty! But how, as the low fuel light hadn't come on? I looked under the tank to find the low fuel sensor disconnected!
Presumably left that way during the various meddling by either the dealer or importer.....nice work guys.
Improvising a fuel transfer from the other bike, thankfully a carb equipped Harley, we were soon on our way to the garage.
Since then, I've managed to get another 1000 miles on the bike with no further issues, touch wood. I'm just grateful to have it back in my possession and out of the hands of the professionals!