Sorry everyone about the downtime today (twice).
Basically the server crashed while on the backup server. It corrupted the database. Normally this would be fine, but before I had chance to restore the database it started making a backup (replacing my good backup DB copy!).
To prevent this in future I have ensured the DB is scanned for errors before backing itself up. Also I reduced memory allowance on the backup server (VM) to prevent it crashing again (was out of memory).
For any non-geeks who don't understand that, don't worry