I would be interested in a UK Hackathon, and there are a fair number of heavy-duty UK techies, I suppose the way forward would be a weekend event, and the crux would be, primarily, suitable premises.
* Good wifi, plenty of mains outlets. * Food and drink * Presentation facilities * Cheap accommodation * Reasonably easy to get to (this is always a problem in the UK of course)
Perhaps the best way is to start small but scalable?