In reply to Chris Harris:
I think you're supposed to use the address of the place you are actually living at and update them in a "reasonable" timeframe.
Banks and utilities probably don't care so much - DVLA, doctor (if in another surgery's catchment area), maybe other places, will.
However, a mate of mine that lives in Germany uses a friend's house here as his "UK address" for his old bank accounts and so on. As far as I know, it's never been queried.
In your scenario, you're probably fine.