Passengers who are fully vaccinated arriving into the UK from non-red list countries are able to take a post-arrival lateral flow test.
Since 31st October, eligible fully vaccinated passengers arriving into the UK from countries not on the red list will have the choice of taking either a lateral flow or PCR test on or before day 2 of their arrival.
Any individuals with a positive lateral flow test will be required to book a free confirmatory PCR test and isolate for 10 days. If the subsequent mandatory confirmatory PCR is negative, then the isolation period can end.
Those that have already bought a PCR test do not need to buy another test. Lateral flow tests for international travel must be purchased from a private provider as NHS Test and Trace tests cannot be used for international travel.
All travellers must complete their passenger locator form prior to travel, including providing a test booking reference number supplied by a testing provider.
Individuals who are not deemed as fully vaccinated must still complete a passenger locator form, take a pre-departure test, have booked a PCR day 2 and day 8 test package and complete 10 days self-isolation on return from a non-red country.
Full article: https://www.health-ni.gov.uk/news/lateral-flow-tests-be-introduced-fully-vaccinated-non-red-international-arrivals