Calculation of capital gains tax on spin off shares

I had bought shares in United Technologies which has spun off 2 companies Carrier Global and Otis Worldwide and allocated me shares in each of the spin offs. When I sell shares in each of these, please advise on how to calculate the capital gains in each case. Does the entire value of each spin off holding count as capital gain seeing as I did not pay for them?

Hi,
Please refer to guidance at HS285 Share reorganisations, company takeovers and Capital Gains Tax (2024)
Thank you.