Welcome !! My twopenneth worth :
Say I wanted to fly from Compton Abbas to Yeovil (Westlands). Do I have to file a flight plan for this? Do I have to talk to anyone to let them know what I'm doing?
You don't have to file a flight plan, but I think Yeovil is PPR, so you'd have to phone them prior to take off and get permission to land.
Say it's a cloudless day, how high am I allowed to fly before I begin to infringe on 'someone else's' airspace?
In that area, it's all open airspace (apart from the normal Class C airspace above FL195 - but if you get to 20,000ft in a light aircraft, that'll be the least of your worries !!)
At what point do I have to make contact with Westlands - when I leave Compton? Or when I'm a few miles away? What about the Yeovilton MATZ - am I allowed to fly within that area, or do I need permission?
Looking at the map, you'll go straight through the Yeovilton AIAA (Area of Intense aerial activity), so talk to Yeovilton as soon as you can. They'll take care of you - lovely people that they are (
). As for a MATZ penetration, if you need one, just ask 'em
Having said that, someone will come along in a minute and point out my mistakes !!!
Most of all, enjoy it !!!