The things that will affect the average VFR flight in the UK tend to be glider comps, aeros comps, air shows, kite and model rocket flying (!?) and the odd temporary danger area. These sorts of things tend to be published quite a long way in advance so as long as you check the NOTAMs when you're doing your briefing you'll be informed. There are obviously going to be the odd occasion when something happens while you're airborne, but that's what the radios for...