I haven't got all the way through this and indeed not given it the most attention, but there seem to me to be some deeply questionable assertions in this piece.
It spends a lot of time trying to pin a significant root cause for Brexit on Gordon Brown's decision not to join the Euro, and it also describes the US/UK subprime mortgage crisis which indeed the UK was highly exposed to, without any real (at least early) mention of the massive European credit crisis, which it was not.
I do see what it's trying to do here - in too deep to get out, too big to fail. But in this alternate reality where we joined the Euro, we probably still would have been heavily exposed in our own way to the US-initiated crisis and then, as the US recovered, exposed again to the EU one, and honestly at that point I think Brexit and returning to the pound would have looked like a pretty fucking good idea all round.
Perhaps this is for a different thread.