High marginal tax rates in the UK are mainly hit at low wages (when you come off universal credit and get taxed at 75p on the pound, when you're repaying your student loan when you get an extra 9p/pound, when you have two kids and the loan at 50k when you get hit by 69p (about to be 72p)

Once you're at say 200k, your marginal rate (as you'll have repaid your loan in the first couple of years) is 45%

Someone on $500k in CA will pay $210k in taxes. Someone on $500k (£375k) in the UK will pay $220k (£165k). That's not a massive difference.

Sources https://listentotaxman.com/375000

https://smartasset.com/taxes/california-tax-calculator