// Question is - does anyone know how I go about 'joining up' for a bit? //
Unless I've missed something there's nothing formal yet, so at the moment the only thing to do would be to speak to a local school to see if they are interested.
On the other hand, in September I think there's a plan for some National Tutoring Scheme, and when further details are announced you might want to look into that. As best I understand, certain (as yet unknown) tuition agencies will be called upon, but I'm sure there wouldn't be a problem with a former teacher jumping into one of said agencies and getting involved. Given that it would be a £billion-odd scheme I don't think pay would be a problem either.