Perhaps a better place to formulate our governing document, our bylaws, our territory, &c. would be on a website for the chapter. I understand James already has purchased suitable domains - a Wiki could be placed here. This would not be new - I believe the German wiki already has a website? Further, something tangible (however tangible a website may be) may be the catalyst necessary to kicking this project off the ground...
I don't think there is yet anything which needs to be kept confidential, so it makes more sense to simply use Meta for this rather than needing yet another wiki to check on.
http://meta.wikimedia.org/wiki/Category:Wikim%C3%A9dia_France and http://meta.wikimedia.org/wiki/Category:Wikimedia_Deutschland show that these two chapters did at least start off using Meta for discussion and documentation. For the French chapter, the project namespace on the French Wikipedia was also used for a lot of this, but I wouldn't recommend that since it implies the chapter is focusing on a specific project and language rather than all Wikimedia projects in all the languages of the UK.
Angela.