To be honest, I doubt you could help all that much... But I know how you feel - I'm a member of SJA, and a few of us have mulled over the idea of taking an Ambulance down to assist. Decided by the time we'd arrive there would be little for us to do, and we'd just get in the way (especially as we aren't involved in the Major Incident Plan for London.) So unfortunately, we just have to sit and wait. It sucks.