Farmer was ok, albeit bemused, with us parking our bikes (engine, not pedal) at the gate before the yard. He may not be with cars parked there. I would stop and ask on the way up, given the current situation I'd be prepared for a refusal and turning around.
Access is walk in. From the Drumhouse, there's a non-obvious route through the trees that becomes more obvious as you head up it. Check google earth to give you an idea. One wet adit just beyond the stile at the top of that path, and a few quarries and a crawly hole with a skylight, going to a blind wet trial that goes for a few feet in the back of it. Continuing along the hill, rather than up it, from the drumhouse, there is a collapsed adit and some marshy ground in front, but we didn't investigate if it went as we didn't have wet gear.
Searching for the ever elusive Underground Titty Bar.
DDDWH CC