Backdating UK residency once it has been acquired

I am a British citizen moving back to the UK from Germany in February 2025, i.e. just before the tax year ends, and I intend to remain in the UK for many years. I've read all of the RDR3: Statutory Residence Test (SRT) page and I want to understand whether once I become a UK tax resident, if beginning of my tax residency be backdated to when I moved back to the UK and started working? For example, I was looking at RDRM11370, "all or part of the 365 day period falls within the tax year", so if I manage to work for 365 days and at least one of those days was in 2024/2025 tax year, then I am a tax resident for that period (assuming also the 3 hour minimum..). I can imagine a scenario where I start working in February 2025 and then work for 365 days, I could perhaps be tax resident also for 2024/2025, but it would only be clear perhaps in 2026. For me the implication is whether or not I will be able to open an ISA on my return to the UK (requirement: UK resident) and whether or not I will be able to use my CGT allowance in the 2024/2025 tax year. I know I will become a UK resident, I just want to understand this period beforehand in the previous tax year.

Hi
HMRC cannot adviise you on  your residence as this is for you to determine based on the guidance available. As you have already used the RDR3, you should also consider Residence: The SRT: Split year treatment as you are returning to the UK. This confirms the date from which you are classed as resident to allow you to see if you are then resident or not for 24/25.

Not HMRC...as you return permanently in Feb 25 you are treated as tax resident from arrival (on the basis that you meet requirements and will be resident for 25/26 and dont leave again before 5/4/26). As a result you would be ok re ISA for 24/25 (treated as tax resident from arrival) and also entitled to CGT allowance regardlesss (on basis that UK citizen?...if so you dont lose allowances in the UK even when outside of UK)