CGT - National Grid

[js3]

I've inherited some National Grid shares. The deceased owner died shortly before the rights issue in May 2024, but I received the shares after the rights issue. The rights were not taken up while administering the estate. I want to calculate the CGT base price for the shares I have acquired.

The rights issue issued 7 rights for every 24 shares.

My understanding is that the base price for CGT purposes for these shares is given by a formula of the form N x A x B / (B + C) where
N is the number of shares I have inherited
A is the share price on the date of death (or the date before or after if the markets were not open)
B is the opening price of a share on the day the shares went ex-rights
C is 7/24 of the opening price of a nil paid right on the first day of trading of these rights.

Are the values for B and C available somewhere?

[pawncob]

https://www.google.com/finance/quote/NG:LON?window=6M