Tax payments for our first year in UK

Hello, I need help understanding how to navigate our new UK tax situation. I am a UK/US citizen and my wife a US citizen here in UK on a spouse visa. We moved from California at the end of March 2023 intending this as a permanent move and will be considered tax residents for UK tax year 2023/24. We are both retired and our only income is foreign pensions for us both and a small amount of savings interest and modest dividends. We individually make more than our UK personal allowance. In the US we file as married filing jointly and understand that in the UK we will file individual self assessments and we have both registered for that. I have my UTR but my wife still awaiting hers. I'm confused as to how to navigate this first year as I was told we should pre pay some of our self assessment UK taxes before the end of the current US tax year 31/12/2023 even though we have not filed a self assessment and that payment would off set any US tax liability when filing our US return. I was also told by HMRC that the opposite was true. Pay our US taxes for 2023 and use that as credit towards our UK tax liability. I'm very confused about how best to comply with all this. Then others have mentioned split year treatments and my head spins. Would appreciate any advice or direction to some information on all this. Thank you.

Hi Brian Courtney,
As you did not move to the UK until the end of March 2023, under the 'split year' rules you would only have to declare (in your 2023 return) any income received between the date you arrived and the 5 April 2023.
When completing your Self Assessment Tax returns in the UK, both you and your wife can claim any Foreign Tax Credit Relief due in(respect of any US tax already paid) in the Foreign pages (SA106).
As regards your question about Self Assessment 'payments on account', you may find the following guidance helpful:
Understand your Self Assessment tax bill
Thank you.