Have you checked UCAS extra now to see what’s on there? Might give a little indication of what might be available in clearing. It doesn’t exactly follow I know, but I’ve looked for some unis just to get an idea as I’m applying next year. Two of my RG choices are on there, or were.
Given the competition for courses, I should think the top RG are unlikely to be in clearing. I read an article today that said the top 12 RG are rarely in clearing for any courses.