Tax Treaty

I know this is a dumb question, so please be kind.
I keep reading in posts about "entering the tax treaty". How do I tell HMRC and IRS that I want to use the treaty? I've never seen the question asked on any tax form. I just assumed I fill out the appropriate 1116 forms for Foreign Tax Credit. I see nothing on HMRC when I do my self assessment. I am aware that I pay UK tax on foreign income, and then claim FTC. I am a dual US/UK citizen, UK resident, who lived in USA for over 30 years then moved permanently back to the UK. I'll be getting SS in a few years and know that is taxed only in the UK. I have an IRA in the US that I am withdrawing from, and that is why I need to use the treaty.
Additionally, do I have to pay US tax upon each withdrawal from the IRA even though I won't owe any tax after the credit is given.
Thanks for your time. This forum is invaluable.

I know this is a dumb question, so please be kind.
I keep reading in posts about "entering the tax treaty". How do I tell HMRC and IRS that I want to use the treaty? I've never seen the question asked on any tax form. I just assumed I fill out the appropriate 1116 forms for Foreign Tax Credit. I see nothing on HMRC when I do my self assessment. I am aware that I pay UK tax on foreign income, and then claim FTC. I am a dual US/UK citizen, UK resident, who lived in USA for over 30 years then moved permanently back to the UK. I'll be getting SS in a few years and know that is taxed only in the UK. I have an IRA in the US that I am withdrawing from, and that is why I need to use the treaty.
Additionally, do I have to pay US tax upon each withdrawal from the IRA even though I won't owe any tax after the credit is given.
Thanks for your time. This forum is invaluable.

In the US (with some exceptions) Form 8833. In the UK, HMRCs non-residence pages and/or white space.

Thanks!

In the US (with some exceptions) Form 8833. In the UK, HMRCs non-residence pages and/or white space.

Does my partner need to complete the form 8833 in US before moving on her visa this week? This is for everyone right? And tax returns must be submitted in US each year as normal.