This is a question that crops up now and again from clients who perform some of their business activities at home.  Generally speaking, if the room used for the business is also sometimes used as part of the home (e.g. as a guest room, or for watching television / looking at social media) then it will not result in you having Capital Gains Tax to pay.  If, however, the room is used exclusively for business purposes, then it might result in a Capital Gains Tax liability.  But even then, you would have to make a very large gain when you sell your home for the business element to exceed £12,000 (2019/20) and leave you with a Capital Gains Tax bill.