Donating land, property or shares
You do not have to pay tax on land, property or shares you donate to charity. This includes selling them for less than their market value.
You get tax relief on both:
Income Tax
Capital Gains Tax
...
Income Tax relief
You can pay less Income Tax by deducting the value of your donation from your total taxable income. Do this for the tax year (6 April to 5 April) in which you made the gift or sale to charity.
How to claim
If you complete a Self Assessment tax return, add the amount you’re claiming in the ‘Charitable giving’ section of the form. This will reduce your Self Assessment bill.
https://www.gov.uk/donating-to-charity/ ... -or-shares
I think the question is just whether "Income Tax relief" means relief on 'pure' income tax, or relief on all the tax you pay in a self-assessment income tax return. But, thinking about it, the Gift Aid wording "they must pay enough Income Tax and / or Capital Gains Tax to cover the tax" which they use repeatedly looks promising - if Capital Gains Tax can be counted for the purposes of "did they pay enough tax for the Gift Aid reclaiming process?", then you'd hope they use the same calculation for share donations.