Thanks for the advice guys.
I may just write this one off to experience and start again on m/m.

I always take York and Brittany in the first couple of turns, then turn to Wales before heading up to Scotland. For some reason I left the Scots alone thinking they would be their usual apathetic selves, but I was shocked when a stack of screaming clansmen turned up outside of York - oh dear.

Next time I'll be ruthless whilst William I is still alive, and take the fight to the Scots. His gentler sons can concentrate on securing rebel lands and going on crusades.