yorkshirewolf wrote:The countrys covered on old MOD bunkers/pillboxes ROC posts, but most of them are in a pretty bad state and they're getting either filled in or bulldozed because of the 'urban explorers'
I've worked on a few farms so have been in a few of the old ROC posts, I've also spent some time exploring the old war structures in Normandy, and i can tell you that unless there is a complete breakdown of society/law/order/civilisation and the marauding gangs are going door-to-door then i'll be much happier, secure, comfortable and better equipped in my house.
Nearly all of the structures i went in were cold, damp, mouldy, urine-soaked, had a collection of used condoms/needles and were generally pretty grim, so there's no way i'd want to spend any time in a concrete box the MOD abandoned long ago - for good reason! Not when i can use a tent.
They are fun to explore though...
EDIT;
Anyone interested in the old war structures can have a look at subterranea brittanica http://www.subbrit.org.uk/
The MOD didn't abandoned them because they were cold and damp (thats never bothered the MOD before
) they stopped using them because they didn't need them. And yes a tent is going to be more fun.... unless someones shooing at you... , then cold and damp might start looking like a good idea... 
It's going to depend on what the OP's bugging out from really. I know around Southampton-ish theres lots of disused tunnels that might be a better bet than a pillbox, more room and more ways out usually.