"a newly independent England will have an awful lot of searching and potentially very expensive defence questions to answer."
Well that assumes we go for the same level of kit etc as we use now. Operate the current Trident fleet out of the East Coast US for a fee for a few years - I could see it being a great excuse to scrap the Successor programme (thus pleasing everyone from the Treasury to a lot of voters) and maybe building a few more Astutes to keep Barrow busy. You could shop for warships anywhere without having to build them expensively in Scotland. The RAF comes south - maybe having to accept "austere" basing for quite a while without all the expensive support bells & whistles but it's only a few squadrons these days. The Army? Not many up there so back to Catterick or disperse more to the Middle East, Cyprus etc
It's a sad fact but "expensive defence questions" are normally only answered one way in the UK these days - cut the capability.