[Direct Flight Information from London to Incheon]
Since 9 May 2021 there has been a limited resumption of direct flights from London to Seoul. These relief flights operate weekly, with Korean Air and Asiana Airlines operating the route alternately. Occupancy is limited to 60% of the aircraft’s capacity, and 90% of the tickets sold are reserved for Korean nationals. Non-Korean nationals, including British nationals, must be in possession of an A1, A2, F4 or F5 visa. Other types of visa will not be permitted. You should check the schedule and your eligibility to travel with the airline before booking, and remain aware of the quarantine requirements on entry.
source : https://www.gov.uk/foreign-travel-advice/south-korea/coronavirus