Thanks for the replies everyone. Assumed they would be able to, but wasn"t totally sure given the different branding of the Gs.
Interestingly, the Luton G isn"t on the list of exiting casinos when you select which one you"re a member of (although the Thanet G is!).
I remain to be convinced whether they will have done anything with on-line membership forms - Luton certainly ignored it when I joined there.