Hi Bodhi,
Anyone, who is resident and domiciled or deemed domiciled in the UK, must declare their world wide income, arising in a tax year, to HMRC.
This includes the interest arising from your IRA distribution, regardless of whether it is remitted to the UK or not.
This is done via a self assessment tax return and supplementary page SA106, where the income is declared in pounds sterling.
The interest from your IRA account is added to your UK interest and the appropriate savings rates applied.
Anyone who is not domiciled in the UK, has the option to use the remittance basis, where they are only taxed on their UK income/gains and any remitted income/gains.
Have a look at section 9 of
Residence, domicile and the remittance basis: RDR1
Thank you.