Depending on it's actual age, I wouldn't say it was a volcano per se, if natural it is possible that it was the result of a volcanic upheaval, there are quite a few hills created that way after all(the majority of them...lol) ...from the 1st pic, it looks very similar to Coopers Hill...not the one of poem and legend...but the one close to Bletchingley which is visible from the M23(between Gatwick and the M25).
Apropos of nothing...some "natural" hils created by volcanic action have natural tunnels created by the bubbling and cooling effect.....and might well have been used as a ready made shelter/burial/sacricial chamber. All that said it looks a great place to visit whether natural or man-made.