It seems to me that in general terms that London regards Cambridge Festival as its' Folk Festival
Really? I must be imagining all the London folkies at Sidmouth.

but the London scene has (if I can put it rather clumsily) seems to cater for a more cosmoplolitan audience
Considering how Anglo (or at least Anglo / Irish) centric London folk clubs are I hate to think what the provincial folk scene is like. Maybe that explains all the "I only go to sessions" comments we see on Mudcat.