My apologies for over-estimating UK tax rates. The UK does have still some incredibly high marginal tax rates for those are elderly and lose higher rates of personal allowance for having higher incomes, or those on child or pension tax credits and lose these for receiving greater income.
The exact rate is not always too material except to say that the last contributor is spot-on to say that in high tax states (such as New York, Georgia and California) effective tax rates can be higher than in the UK.
There are significant differences though, in that the US system generally gives many more tax deductions than the UK; but the UK gives significant deductions for housing & commuting costs for some folks who come for less than 2 years and those with non-UK workdays who come for less than 3 years. As a consequence, people on assignment here can often end up paying far less than back home.
Also, the US charges tax on worldwide income and gains, while for almost all readers of this site the UK only charges tax on income and gains arising in or remitted to the UK. So those with reasonable levels of investment income can save a bunch of taxes while living in the UK (because for those of us not domiciled here, the UK only looks at worldwide income when assessing child and pension tax credits).