Also important to realise that 50k£ is 2x the national average wage. So for more than half of the population it's nothing to scoff at.
The UK is also in a bit of a funny place when it comes to immigrating to the US - due to a lot of American businesses having satillite offices here and a lack of specific visas for Britons, you're going to have a hard time finding a company that will be willing to sponser and relocate you.
Another really important factor when looking at the UK labour market, specifically in London (because my experience with it is there, but this could be true for the other major UK cities), is that contract roles are much much much more lucrative that FTE (or at least, they have been prior to IR35). If you're a mid/senior contracting at a bulge bracket bank you could expect a ~500£ day rate. 500£ * 282 (working days - some holidays/sick/national holidays) = 141000£. If you run that into your contracting LLC, rather than take it through PAYE, you can cut your effective tax rate by a big margin depending on how you spend your money - so even more cash that you would be FTE on the same wage.
I think you might have done your subtraction the wrong way round. Or do contractors really work an average of 5.4 days a week?
That’s a not uncommon rate outside of banking too in London.
Transfer becomes easy then.
Solid experience and skills will get you offers around 100k GBP from bigger, well funded startups and if you want to sell your soul to the finance industry you can get like 300k GBP total comp. Those are both real offers I’ve had in London.
What do you mean when you say the finance industry? It's a pretty big field. Is an online bank the same as some real time trading platform? Also, why is it selling your soul? Is Google / Facebook "better" (that is - more moral) than a fintech company ?