I have already tried and checked the following:
1. new batteries in both keyfobs
2. reset both keyfobs by pressing the lock button 5 times
3. checked that the central locking button locks and unlocks all doors
4. the battery was a bit low (it has sometimes been flat in the past as the car is more for looking at these days!) so I put it on the charger and now get a reading of 12.4V, which I would have thought would be adequate not to upset the more delicate electronics
5. battery reset
6. checked fuses 5 and 13 for the BCU (Body Control Unit)
7. the bonnet switch is ok as the horn gives the usual warning blast if the car is locked with the key with the bonnet opened
8. the fuel flap does not lock (but it is not expected to when the car is locked with the key)
9. the interior light comes on and goes off automatically as it should and the door open warning on the IPK (Instrument pack (IPK from the German)) works for all doors, bonnet and boot
10. it is not caused by RF interference because it’s parked in the same place it always has been, it happens everywhere and is not intermittent
So I'm now at a bit of a loss. Any thoughts gratefully received.
Steffan