It seems a good idea - but many of us would want some decent beer as well as mulled wine (terrible stuff to sing on). London folk events can be a bit variable (I was one of the organisers of the St Georges festivals at CSH in the 70/80s). I doubt if you'd get any "Londoners" there who aren't already members of the folk scene. One tip if you want to get london folk clubs involved, try and get some representatives from them onto the organising committee.

One other group of people who might be interested in supporting the event are the remnants of a now defunct club Capital Folk who still have regular get-togethers. Try talking to Dave West (usually at "Sharps" on Tuesday night, but I do have his phone number if you want it).