My central locking was slightly intermittent and then it decided to stop altogether. I didn't have any problems with it locking by itself or the boot opening on its own, but my solution may help these problems. I thought it was my battery so I replaced it, but it still didn't work. I then found this info about resetting/reprogramming the central locking:
Insert key into ignition and turn to ignition and back 4 times in quick succession.
You will then hear a chime which indicates you are in the central locking programming mode.
remove key and press the lock and unlock (although I only needed to press the lock) button on the remote.
You will then here another chime and it should be done.
My central locking works great now with no issues as yet.
Hope it helps, it saved me £45+VAT for a new remote and £68 + VAT my local ford dealer were going to charge me to program it (they probably just use the method given above!). Perhaps this should be a sticky along with info about the central locking fuse and where to find it.