Well I think I'll post some (initially not very helpful) clues for some of the outstanding ones...
1. - Rather surprised this hasn't been guessed by those familiar with the southern half of the UK.
4. - Don't know much about this cave myself as it's up North, certainly not been there. I believe it's reasonably well known but little visited.
5. - This is an old survey but represents the route most would take (and was the route I took). I think a few minor side passages are omitted.
6. - Perhaps a little obscure, not one of the 4 major caving areas in the UK.
9. - Definitely obscure, but well worth a visit if you're in the area.
13. - Down South. Again a little surprise this hasn't been guessed.
18. - Popular easy cave
Better clues tomorrow night if still not guessed.