Man blackout != energy starved, you can have blackouts cause your infrastructure is attacked or just random natural disaster, look at energy prices compare it to China or even US not even speaking about oil rich countries.
Finance in UK is indeed legacy it is mostly big old banks there is still a bit of fintech and ofc. head funds, but UK is bleeding both talent and market share to CN and US. Not even speaking about tech salaries 10 years ago London was one of the top paying places for finance tech, now it is (ofc.) USA and CN (especially with cost of living).