Hello there Steve,
My apologies for not replying sooner, we had given up since we did not receive your reply on Sunday at all! Ah well, thank you now.
I have gotten to the stage where I can now start the car normally, but the key is immediately 'spat out' of the ignition barrel. It seems unable to hold it now for some reason...
So long as I push it back into the barrel immediately after I press the start button to stop the engine, I seem to be OK.
My impression is that it is the barrel area, not the key that is at fault and shall follow this up with BMW as soon as I can.
it is common for the key slot/receiver to fail on this model. you likely need to have yours replaced.
Please let me know if you have further questions. Please do not forget to click a positive rating as this is the only way I receive credit for my answer, thank you. Best wishes with your vehicle.