"any sign of a causeway or a spiral path to the top?"
.... Couldn't see one. On the other hand, I thought there was just a hint of the slopes having multiple faces, like Silbury, (Pete and Jim?)but the trees and overgrowth make it very hard to judge. It needs clearing, and some fly tipping removed.

Of course, if it is a proto-Silbury it could be of similar form to one of the earlier Silburys.

Did Pete mention, there's quite a large Sarsen there?

One thing, if you view it from a long way back at the right level and in line with some telephone wires, it's clear that the top is very precisely level.