Exchange rates for Capital Gain calculations

Hello! I have a couple of questions about excange rates for Capital Gain calculations. My situation as follows: 1. I received USD in 2020 from sale of some assets in USD ( appropariate exchange rate was used to declare conversion of USD/GBP at the time for tax calculations) 2. I used thiese US Dollars (aquired in 2020) to purchase shares in 2021 3. I sold the shares in 2023 4. I partially converted USD into GBP in 2023 and rest of the money was left in USD. I have a couple of questions regarding my capital gans calculations: 1. Can I use the exchange rate USD/GBP for 2020 (when I actually aquired USD and not when I bought the shares, using these USD) to calculate the purchase price of shares in GBP? 2. When I sold the shares in 2023, I made a partial conversion of my USD to GBP. Can I use actual conversion rates for the converted amount and a spot rate for the remaining amount (which was not converted to GBP.) ? Thank you in advance for your help!

Hi,
You would use the exchange rate in use at the time of acquistion and disposal, not when you changed the currency. For capital gains purposes, it is the cost of the share, when it was bought. The cost of converting the currency is not part of capital gains. You have to bear the brunt of the gain or loss on that exchange yourself.
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. For your convenience, there are exchange rates here:
Exchange rates from HMRC in CSV and XML format
and for older rates here:
Foreign exchange rates and spot rates: 1 January 1989 to 31 March 2009
You are free to use any of the supplied rates or one of your own choosing. 
Thank you.