I got directions in the end - off an old dear who lives there..
You park in 'long field' (between the two tracks to the houses) and walk up. It's in the field at the top. There's a gate into the field it's in. Long field can't be missed, it stretches uphill and is very. . erm . . long.
I think this must be the least visited of all the complete undamaged circles ever.