JDK--erm, where are the bunkers you mentioned near Weston then ? I used to fly out of there in my younger days so am familiar with the area---just curious.
On the S side of the A4095 just after you have gone W from the B430, about 100yds from the junction. There's two bunkers, hidden in trees and with what at a glace looked like a Perimiter Track concrete roadway with them. Despite their distance from the airfield (about 3 miles North) they were obviously military, and when I'd checked up, nothing to do with Weston. Also they won't be evident from the air.
Turns out they were the ghastly bunkers for poor ROC (see here:
http://www.subbrit.org.uk/rsg/roc/index2.shtml )
Cheers!