Reporting capital gains on US inheritance

In June 2023, I received an inheritance from my grandmother, who was a US citizen and lived in the US.
As part of this inheritance, I received an investment portfolio. I'm trying to report capital gains I have received from this investment portfolio, but I'm not quite sure how to do the calculations. Many of the stocks that have been sold have an acquisition date that precede my ownership of the portfolio.
Do I use that acquisition date and the value the stocks had at that date when calculating my capital gain?
Or do I use the date of transfer (June 2023) and the value of the stocks had at that date?
Thanks for your help!

Hi,
You would use the market value of the stock on the date you inherited it, as the acquisition cost. This will be the same value applied to the stock in your grandmother's estate. This sum is converted to GBP sterling using a just and reasonable exchange rate in use at that time. The disposal value is also converted to GBP sterling, as well as the disposal costs, using an exchange rate in use at the time. The disposal value minus the allowable costs, give you the gain or loss.  
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
You can see 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.