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.
>> the best advice I was given was to ignore the 'beware of the bull' sign.
If you're looking for stones and you're in approximately the right area look for the beware of bull sign. That's the field with stones and no bull in it :-) <most of the time>