Just trying to get my head around dns settings and google apps.
In order to get www.mittenview.co.uk to be hosted at google apps and to use mittenview urls had to:
1) Add a CNAME value for www pointing at ghs.google.com. (trailing stop is important) in the DNS table at plusnet
2) Add a mapping from www.mittenview.co.uk to http://sites.google.com/a/mittenview.co.uk/Home
3) Make site publicly shared (Open site for editing then - Site settings > Share This Site > Check "Anyone in the world may view this site")