Although I have decided not to take any unnecessary risk by using the field for T/O I did want an answer to my question.
Today I received a call from the Garrison Sergeant Major and after a brief but direct grilling I have been told that there is no issue flying over the garrison.
A few rules (all the suspected): no photography, No Video, Avoid any MOD aviation, Check NOTAMs .....
Result!
PPG Vs. MOD 1 - 0
Duncan