Yep - had the same issue on my 4/4. Diagnosed by the excellent Keith at BHM. Wiring for seat belt 'nanny light' gets trapped in seat runner as you adjust it. Hit a big bump and the wire strips its plastic coating and shorts out on the metal seat runner. This wiring shares a common fuse with the dash instruments.
If MMC added a couple of pence worth of cable ties it wouldn't have happened...
