I second what Stu said above; in general British cavers don't take this subject seriously enough which is probably because our caves are fairly warm & forgiving compared to some. If a caver can't manage the weight of a little bit of emergency kit then they should eat more Weetabix in the morning.
Few observations: as someone mentioned group shelters/kisus are great & they've been obligatory equipment for anyone involved in exploring the Dachstein caves for the last 15 years when we realised how appallingly useless those flimsy little survival bags/blankets are in Alpine potholes. Lot warmer than you might think. And when you climb out into a blizzard you'll be doubly grateful that you don't have to crawl into your shredded bin bag! I sew on a couple of loops along the top, attach tiny krabs & suspend a length of cord across the chamber/passage etc & it then turns the clingy sack into a comfortable tent that doesn't get too damp inside.
The classic method of using the big orange survival bags (as someone else mentioned) does have it's drawbacks. In an ideal world you'd be fresh & awake when trouble hits but the reality is that you'll probably be tired, wet, hungry, sleepy & very, very cold. Under those circumstances it's easy to start nodding off, chin drops to chest, start inhaling fumes, legs slump slightly, flame starts melting plastic, more noxious fumes, wake up gibbering in the cold, burn oversuit whilst trying to drag the excess plastic over your legs which is now tricky because you're trapping it with your ass. Hmmn, they don't mention that sort of stuff in the books....
