What's the latest POD for a balkanized Britain? I for one don't think its possible to balkanize Britain more than it is (England, Scotland, Wales) after the Napoleonic Wars, but my knowledge of British History isn't good enough to speak confidently beyond that.
I think that if you make a few changes in Scottish History, you can get a greater Highland/Lowland divide, what with them speaking two different languages and all (Gaelic and Scots). Then through a bit of bad luck you prevent the clans unifying, and voila!, a Balkanized Highlands. But how can you do that for the rest of Britain? What's the latest possible PoD?