London effectively subsidizes the rest of the UK,
You need to differentiate between Greater London, and the City of London
Does not change the argument at all.
I'm not completely sure on this but historically, doesn't the majority of money into London come from outside of Europe? From looking at the last financial crash, a $700 billion insurance company which served credit default insurance to the UK and US (and a few of the US banks went bankrupt because of it).
The depreciation in the value of sterling i'd agree is probably due to more to the uncertaincy over brexit and not a direct impact. There were also articles scaring people out of investing into the UK by adding clickbait headlines of "the UK will go into recession if they vote to leave the EU" (which didn't happen but probably scared people from investing anywhere near the country after the vote had been declared). And if you look at the data, we were already in a downtrend to start with. In 2013 the pound was at $1.70, in 2015 it had reached $1.50, brexit may have amplified things but I'm not sure it provided the activation needed.
I think we should all at least be in favour of keeping healthy diploamtic relationships with the rest of the world and helpiing the european governments (where necessary) in security and privacy protections (as was done with GDPR).
Europe is a lot different from the USA, I don't think the continent can be joined into one huge supercountry, and if it can, I don't think it benefits from the UK being a part of it.
As I see it, and I was thinking about this before, the biggest issue we have was probably the Queen not assessing if the UK government had a clear strategy for leaving the EU (because it clearly didn't) she has successfully blocked things parliament wanted to put through in the past (such as the ability for them to declare war) so I don't see why they wouldn't have put more scrutiny into the details of what was going to happen once article 50 was triggered.
The UK is still pretty strong as a country and as one of the "financial capitals" and a place where large quantities of investments are placed into housing...