CM is correct (as always!): one bitlet to add - you *must* file a flight plan for any flight crossing an international boundary. (Well, there are a few tiny exceptions, but if you always do it you won't get surprised).
I regularly file Y out and Z back when going to France. It's amazing how often the IMC becomes VMC just before the zone boundary :-)
Filing a VFR flight plan in the UK is usually a waste of time - nobody enroute gets it anyway.