Few points of clarification.
Yes Drws Cefn is one of several entrances to Ogof Draenen - there are many other points in the cave very close to the surface. It was dug open many years ago by myself and other Chelsea members - the late 1990's if memory serves me correct - prior to the current landowner buying the land. The cave has been open most if not all of that time. It was connected to Draenen a few years ago by other cavers. It is not a SSSI - Siambru Ddu is, but Draenen is not (yet) scheduled, but it is written up in the Geological Conservation Review (Waltham et al 1997- Karst and Caves of Great Britain).
Not everyone on the PDCMG is in favour of blocking Drws Cefn. As a member of PDCMG, my own view is that the entrance should not be blocked but gated with a suitable lock - ideally something
like the Derbyshire key to make it easily accessible to cavers but not passers by (it's within view of a footpath). That is what we should be advocating to the landowner. I really don't think any cave management group including the PDCMG should sanction permanantly blocking any entrance, especially one that has been open for many years and contains a significant amount of passage. Given the amount of caver traffic down Draenen, and the fact that Drws Cefn-Draenen connection has been open for several years, I don't think keeping it open with a suitable gate will negatively impact on the cave (some people's experience of the cave as a 'wilderness' may change though). However, people removing gates and locks is stupid and counterproductive - it makes it far harder to argue the case for easing access restrictions or creating multiple entrances, and does nothing for landowner relations to the extent that its probably now too late to get the landowner to agree to keeping Drws Cefn open. But this has all been aired before elsewhere on this forum.
I'm ambivalent re CROW. However, irrespective of right to roam/landowners, it ought be the nature of the cave that determines the type of access be it a leader scheme/gate with unique key/gate with combination lock/ gate with generic key/open access etc. I think most cavers would agree with that - although most cavers no longer read this forum..! That said, we should be encouraging caving as a sport/science, and if CROW helps make access easier, that may be a good thing. Perhaps a compromise would be a generic Derbyshire-type key for any gated/vulnerable caves on CROW land?