The best way I can see doing this (as suggested by Angela), is to write a first draft on Meta Wikimedia and arrange a meeting on IRC (#en.wikimedia) at a later time to debate wording and such forth.
#wikimedia-uk is more in line with freenode's naming policy, and already registered.
Is everyone happy with people going ahead and starting to write the bylaws at http://meta.wikimedia.org/wiki/Wikimedia UK/bylaws ?
The first draft is at http://meta.wikimedia.org/wiki/Wikimedia_UK/bylaws but with a somewhat Italian bias. :)
Angela