Charity shop purchase

If you buy something wholly and exclusively for business use then you can add it as a business expense aiui. The fact it comes from a charity shop is irrelevant 

OP, are you suggesting that you want to treat a charity shop purchase as a donation and thereby qualify for higher rate tax relief? The answer is ‘no’. That applies to donations only. Though donations can be cash or goods to qualify.

You can treat a legitimate purchase for your business from a charity shop in the same way as other purchases as @nickjb describes.

https://www.gov.uk/donating-to-charity/gift-aid