In reply to Jonshef:
My understanding is that the need for payment is to do with the restrictions within the law regarding access land:
http://www.inbrief.co.uk/agricultural-law/right-to-roam.htm
"Exclusions and restrictions on public access
There are some general restrictions on the use of access land. These are as follows:
...
engaging in any activity which is organised or undertaken for any commercial purpose is prohibited.
..."
(this obviously can be permitted by the landowner, which is where the need for permission comes in)
I wouldn't know enough to say for sure, but my understanding is that it would be different if there is no commercial aspect to the activity. I guess it wouldn't be a bad idea to contact regular users to have an idea of how busy it's likely to be, but if it's a non commercial group partaking in climbing activity on access land, I can't see how anybody can object to you using the venue.
It can be very versatile venue, with plenty of options, depending on what you want to do. I reckon if groups keep to a compact area of the crag, it could easily swallow up 7 groups.