There are a good 5 or 6 mines on your doorstep that don't need SRT (including Dulas mine).
The guy you want (who has been in them all and will probably be happy to show you) is "Rob" who has the username "Sweetie" on the UCET forum.
Also, the trip organiser (Tony) also on the forum knows them well and it would be easy to arrange a UCET trip to one/some which you could come along on.
www.ucet.org.uk
:)
Ian
A door, once opened, may be stepped through in either direction.