Hi HT2023,
Firstly, please note that there is no restriction on the right of UK residents to have offshore or overseas bank accounts.
You therefore do not have to close your existing bank accounts before you move to the UK.
HMRC requires UK residents to declare any interest arising from overseas or offshore bank accounts, but the transfer of monies from an overseas (or offshore)
bank account to the UK has no income tax implications, unless interest or dividends are generated when the monies are lodged in a UK bank account.
As regards split year treatment,detailed guidance is provide at:
RDRM12030 - Residence: The SRT: Split year treatment: When will split year treatment apply
Thank you