Had car back & apparently it's my fault
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BMW say that if, after replacing the clutch switch (which they did the 1st time it went in), the fault still occurs it is down to "customer behaviour".
I have a copy of the BMW service memo that they sent to the dealer. If someone can tell me how to attach an image from my HDD I'll post it.
Used the car on a good motorway run last night & it seems to be working ok but time will tell.