If you organize it there will be at a place and time of your choosing. Best however to try to agree with a few people. Just set up a thread and start the discussion, best with some hard facts of your availability and radius of action.
London is a somewhat convinient place for Europeans in General, since cheap flights are available. Amsterdam was disscussed once, too. But I would be also open for Cardiff, when I am there for business 🙂