Who gets first dibs on the tax on my interest, capital gains and dividends

Hi I am a dual US and UK citizen, residing and working in UK. I have accounts in both US and UK, generating interest, capital gains and dividends. Who gets first dibs on the tax on these passive income? Do the IRS get to tax my US passive income first and HMRC then tax the residual (since UK tax rate is higher)? And does the HMRC has the right to tax my UK passive income first, and because the UK tax rate is higher than US, I should not be double tax on this income? Or can the IRS apply the 'savings clause' to get first dibs on this income? If so, would HMRC get the difference between HMRC rate and the IRS rate? Since US tax filing is due April (with extensions to June and possibly October), but UK self assessment filing does not start until end of US tax deadline, I'm trying to work out my estimated US taxes and pay this before end of the year to hopefully meet the safe harbour rule. But I'm confused whether the 'savings clause' can be applied to my UK interest, dividends and Capital gains, which would make a difference to the estimated tax on the US side. Hope this makes sense.

Hi Global_Kittizen,
The country in which you are resident will have first rights to tax you on your worldwide income.
Foreign Tax Credit Relief can then be claimed in respect of tax paid elsewhere to reduce your liability.
Thank you.