I returned to my locked BMW 118d to find the engine still running after being parked for 7 hours. In my hurry I had not pressed the Off button. My fault of course but I checked with the dealer whether locking the car should cut out the engine - it doesn't. They had been caught out in the same way and it seems it is even possible to drive off without the key in the car once the engine is running, although it cannot be re-started.

Fortunately all I lost was half a tank of diesel, not the car, but I can see no virtue being able to lock it with the engine running (apart from cold mornings possibly) and I feel that the locking button should incorporate an engine cut out by default. This problem would, of course, be impossible with a conventional ignition key.