The US IRA is treated as a pension for UK tax purposes.
You have to pay tax on pensions if you’re resident, or were resident in any of the 5 previous tax years.
You’ll usually only pay tax on 90% of your foreign pension payments (10% is exempt from tax).
You can usually claim Foreign Tax Credit Relief when you report your overseas income in your tax return.
The US tax rates are generally lower than the UK so you may receive a full relief on the UK tax of the pension.