Interesting. Looks like it could just as easily be one of those places a local nutter just devotes their lifetime to carving for no particular reason beyond eccentricity.
nice one, this is up my street - although I havent heard of this (probably due to location), if you're interested in a similar site with carving e.t.c and is famous you have the cave in Royston, which is a great example of a knights templar cave with some history and connections you would expect from these guys>