Upvote:3
This is covered under 4.6 and 4.7 of the Immigration Rules https://www.gov.uk/guidance/immigration-rules/immigration-rules-appendix-v-visitor-rules
V 4.6 Permitted activities must not amount to the applicant taking employment, or doing work which amounts to them filling a role or providing short-term cover for a role within a UK based organisation. In addition, where the applicant is already paid and employed outside of the UK, they must remain so. Payment may only be allowed in specific circumstances set out in V 4.7.
V4.7 relates to not receiving payment from a UK source for any activities undertaken in the UK, with a few specific exceptions that donβt apply to the question posted.
See also the section on the UK in this question Where can I travel for prolonged periods of time while legally working remotely for a company in my home country?