LP Mau

I moved to the UK in August 2023. I was retired and receive a monthly pension from the Hong Kong government, which I believe is not taxable in the UK due to the Double Taxation Agreement between the UK and Hong Kong.I have no other income apart from: Less than £50 per month in bank savings interest from Hong Kong, and Less than £400 per month in savings interest from the UK. I understand that I may need to declare this interest, so I attempted to apply for a UTR (Unique Taxpayer Reference). However, I am unable to obtain a National Insurance (NI) number, as I do not work anymore and therefore don’t meet the requirements for one. Can you advise on how I can proceed with getting a UTR and declaring my income without a National Insurance number? Is there a workaround or an alternative process for someone in my situation? Or do I actually no need to file this tax return? Thank you in advance for your help.