http://www.sypeland.freeserve.co.uk/site10.htm

This is all I could find, it says:

Access to the circle:

"A small parking space is provided at the side of a main road and the circle is well sign posted. It lies only a short distance from the road through a gate and is very easy to reach. The circle in (sic) cared for by English Heritage and disabled access may be possible"

It's that word 'may' that isn't helpful. A long journey to a locked gate is a horrid thought!