I've looked into it before, but honestly I think the SoA is the best investment for a British author, as it holds events across the UK and vets UK contracts as a specialisation (as well as contracts from across the world, of course).
SCBWI British Isles also has a fairly strong presence in
most of Britain for children's writers and illustrators, but sadly they don't have a Northern Scotland network so they're of very little use to me.
(I did offer to join and help create one, but at the time I'd have been the only author in that region, and they needed a bigger group to justify creating a new network. I'm still keeping an eye on things in the hope things will change in the future.)
I'm lucky that there's a strong Writing Development scheme,
Emergents, in my neck of the woods, using art grants and government funding to provide professional beta reading, free workshops and panels, and various other opportunities for new writers. I haven't seen much like this elsewhere, though Brighton has a
very strong programme of mixed for-profit and non-profit schemes in their
The Writer's Place building.