Chilli, both of the gliding sites mentioned do operate outside
their published ours, there's no guarantee that your call will be answered, so you won't know.
As with para drop sites (and they don't always respond) the best
course of action is to avoid the overhead.
And as you're an ex gliding instructor, you should know that
in the vicinity of any club, on a soarable day gliders will be upto cloudbase..................dear chap.
Or you could end up squawking 7700.
7700