To update:
I received the car back on Friday, having had the FEM (Front End Module) replaced. Which sounded hopeful, however, as far as I can work out, the FEM operates wipers, door locks, windows, mirrors etc. Not critical systems, nor anything to do with the ignition.
Secondly, when it was initially tested by both the dealership and BMW, the FEM unit (along with all other modules) showed no errors.
. Now, I am not in any way a BMW specialist, so, for now I am going with it. However, the cynic in me is thinking that they have just picked something to replace, and gone with a big dollop of hoping for the best. When I next speak to the service manager, I'm going to request an explanation from BMW UK as to a) why the unit is responsible for the issue and b) why it is being replaced when it showed no errors.
However, while they had the car, some BMW chimp has managed to put a nice little scratch in my door card on the drivers side. So it will be back at the dealer shortly anyway to have that addressed
.
The saga continues.