Presumably further demands will be made by the devolved parliaments (more than they are already, that is) to expand their fiscal capabilities and devolve certain tax issues. As you said, in the cases of Scotland (even excluding the option of independence) and Northern Ireland given the referendum result, this will become difficult for Westminster to avoid.
They will twist in every direction to stop that happening. The exponential rise and rise (and reliance) on the financial strength of London is something that evidently needs to be stopped. Or at least challenged in some way by other centres in the UK but politicians are frightened to their core about what happens if that particular top stops spinning.
They won't devolve anything meaningful from London (which arguably is the part of England least in need of devolution but the only part that effectively has it) So they won't give Scotland control of corporation tax because they would clearly collapse it and undercut (while Northern Ireland has this, it doesn't count for reasons that you will know all too well)
For as long as 'England' can lay claim to the strength of London (despite demographically, electorally etc being increasingly removed from it as a point of reference) then the perpetual narrative that England 'subsidises' the rest of the UK can be maintained. That keeps parts of England that have, make and contribute f-ck all to the economy in a sense of elevated self importance and reduce the need for any local devolution (because who wants more politicians right?). Lose that and England will turn on itself. And that will end the Union.
Unfortunately that was all fine until the EU referendum exposed these creeping divisions a good ten/twenty years before they should have. London looked at England and England looked at London and they don't like what they see. Everyone needed the EU, the market, movement of people etc. London understood that but the rest of England didn't. As you rightly pointed out, many nations may balk at any deal that feeds almost exclusively into the City of London, particularly if their own nations are structured in a more fluid, federal basis without an over-reaching financial 'heart' (that they can't retrospectively construct)
So you have to start dismantling the City. Or at least setting up domestic outposts in order to make trade deals more favourable.
