OK, time for clarification. I know nothing of Les Williams and he is not involved in the answer.Les Williams, although I can't say I really know him, he's the only les I was able to find on ukcaving and it lead me to Mendip
Therefore jumping to the conclusion that the site is in Mendip is wrong, although there is by chance an apparent Mendip connection.
I saw Les a couple of weeks ago, but it is many years since he was active in cave exploration. I thought maybe it was so long ago that it might not be possible to find him by an Internet search, but in fact not only can he be found, but also there are online references to his digging activities.
It would be more profitable to consider the phrase "something that is three times a cave" in relation to an earlier Cryptic Caves question. You can then plug the answer to that into an Internet search with the forename and activity, this would establish that such a person exists. You then have the answer, but an Internet search on the answer will not confirm it, you will have to look in the Cave Registry to confirm you are right.