Glad you had fun chaps!
FieldMarshall – go past the covered reservoir (not quickly) and as you start to descend, look out for a feint crossroads. The fence has an opening and you will bear to the right. This track effectively takes you around the back of the reservoir and will spill you out by some broken railings with a large stone.
The other side of the fence you are referring is indeed the RMA side but there is public access as there are public rights of way through there.
What I sometimes do, particularly if it’s very muddy, is to follow the circuit of the gravel track on the RMA side to make a loop. This will take you over to the Camberley side and crosses the Wishmoor Stream.
Edit: alternative route avoids The Wall!