A couple of points on MATZ crossings:
1. The controller will ask you to set the Airfield QFE. This is becase the MATZ vertical extent is 3000' above the airfield datum and also that the Military use QFE as a landing datum.
2. Brize Norton and Lyneham do not have MATZs. They are Class D airspace (it says so on your map) so it's no different to crossing an airfield such as Bournemouth. So don't ask for a MATZ crossing - ask to cross their airspace.