CGT on a merged then demerged company

I inherited shares in a UK company in the early 1990's (I am struggling to find the actual date I inherited them). The company has merged and demerged over the years and the share price now is considerably higher than when I originally inherited it. However, I own less shares in the original company now. Merger in 1995 - I'm not sure what happened to my stock holding, I don't think there were any changes. Merger took place in 2000 - I think my shares were converted into the same number of shares in the new company Demerger occurred in 2022 into two companies - I received new shares in both. What share price should I use for capital gains tax UK purposes? I have looked at all the Helpsheets and none have helped me at all on this.

Bumping this to try to get an answer as it seems to have been lost!

Hi CL McG,
As all the one company, it would fall under a S104 holding:
Please  see:
HS284 Shares and Capital Gains Tax (2024)
In particular point 4.
Thank you. 

Thanks for getting back to me, however the companies are not one company any more so I don't think fall into a section 104 holding. The helpsheet is not clear on this at all. The demerger of A created a whole new company B and consolidated the shares in A. I received 1 share in B for each I had held in A, and then, as A was consolidated I received less shares in A. The overall value of A and B together was roughly the same as A was before the demerger. A has since fallen in price whereas B has risen. The gains and losses pretty much cancel each other out. I want to sell all of my shares in both companies to put them into an ISA using Bed and ISA. The total value of both together if I sold them now would be just less than £6k. As my CGT allowance for this year is £3k I really need to know what value, from when, I use to work out my gain/loss.

Hi,
You may need to consider using 2 Section 104 holdings. 
Shares and Capital Gains Tax (Self Assessment helpsheet HS284)
Thank you.