score:3
The appropriate option is a Standard Visitor visa https://www.gov.uk/standard-visitor-visa
Entry, validity, suitability, and eligibility requirements are set out in Immigration Rules Appendix V: Visitor, V1.1 - V4.6
All applicants must meet all of the eligibility requirements in V 4.2. to V 4.6, and an academic seeking a 12-month entry clearance must also meet the additional requirements at V 10.1:
(a) intend to undertake one of the permitted activities in Appendix Visitor: Permitted Activities at PA 11.2. for up to 12 months; and
(b) be highly qualified within their own field of expertise; and
(c) be currently be working in their field of expertise at an academic institution or institution of higher education overseas; and
(d) provide a valid medical certificate if paragraph A39 and Appendix T of these rules apply.
Source: https://www.gov.uk/guidance/immigration-rules/immigration-rules-appendix-v-visitor
Eminent senior doctors or dentists must have been working for a number of years in their profession. They may come to the UK to take part in research, teaching or clinical practice as long as this remains incidental to their employment overseas. See the section entitled Science, research and academia in https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/938632/visit-guidance-v10.0ext.pdf#page33