Ok so I decided to take the plastics around the steering wheel off and have a look. The rattle seems to be coming from a silver metal box which clamps onto the steering column which I'm guessing houses the electric steering lock.

Because I have keyless entry the lock automatically engages about 30 seconds after locking the car. (You can hear it from outside). Then when i unlock and open the car I can hear the lock disengage. I'm guessing that something is not disengaging fully and that it what is causing the rattle.

I tried unplugging the cable which runs into the silver box and the steering lock didn't come on and no rattle. Next step might be the ford garage as this box looks pretty impenetrable.