Here is a guide to the work-related activities that you are allowed/not allowed to do as a foreign national in the UK on a visitor visa (or equivalent). See Appendix 3
https://www.gov.uk/guidance/immigration-rules/immigration-rules-appendix-v-visitor-rulesAlso:
https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/673351/Visit-guidance-v7.0EXT.PDFProhibited activities
Work
V 4.5 The applicant must not intend to work in the UK, which includes the following:
(a) taking employment in the UK;
(b) doing work for an organisation or business in the UK;
(c) establishing or running a business as a self-employed person;
(d) doing a work placement or internship;
(e) direct selling to the public;
(f) providing goods and services;
unless expressly allowed by the permitted activities in Appendices 3, 4 or 5.
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.
and
Payment
V 4.7 The applicant must not receive payment from a UK source for any activities undertaken in the UK, except for the following:
(a) reasonable expenses to cover the cost of their travel and subsistence, including fees for directors attending board-level meetings; or
(b) prize money; or
(c) billing a UK client for their time in the UK, where the applicant’s overseas employer is contracted to provide services to a UK company, and the majority of the contract work is carried out overseas. Payment must be lower than the amount of the applicant’s salary; or
(d) multi-national companies who, for administrative reasons, handle payment of their employees’ salaries from the UK; or
(e) where the applicant is engaged in Permitted Paid Engagements (PPE) as listed at Appendix 4, provided the applicant holds a visa or leave to enter as a PPE visitor; or
(f) paid performances at a permit free festival as listed in Appendix 5.
