Foreign Currency Exchange Rate - Pls kindly tell me

Dear Sir/Madam, I know that we need to convert foreign currency interest earnings into GBP in my tax return. On HMRC website, there are 3 exchange rates for me to choose from ie (1) monthly rate (2) average rate and (3) spot rate. Pls kindly help clarify the following: (Qa) Do I need to adopt a consistency rate on all my calculations? either using (1) or (2) or (3) but not all of them? (Qb) For average rate, HMRC only provides 2 papers in a year (in March and Dec), Does it mean I have to take Dec 2022 paper for calculating interest earnings between April - Dec 2022 and use March 2023 paper for interest earnings between Jan - Apr 23? (Qc) As for spot rate, I can only find 2 papers in the website (March and Dec versions). Is the calculation principal same as Q2? How come I cannot find Singapore Dollar in the tables? Where can I find the exchange rate if it is not listed in the Spot Rate table? By the way, under what circumstances should people take "Spot Rate" in their calculations? (Qd) More importantly, after consolidate all my calculations, am I allowed to choose whatever amount is the "lowest" in my tax return? Look forward to hearing your reply and feedback. Thanks in-advance for your kind assistance and guidance. Cheers

Hi KF@2023,
Under the terms of Self Assessment, we do not provide an official exchange rate and the onus is on the individual to use a just and reasonable exchange rate for each acquisition and disposal.
You are free to use any of the three rate HMRC provides, or you can use a rate obtained elsewhere, such as a newpaper or the London Stock Exchange.
Thank you.