Everyone arriving into the UK, whether they are vaccinated or not, must do a day 2 test
As of 29 November 2021, this test must be a PCR test. You must self-isolate until you have received a negative result
You will need your booking reference for your passenger locator form, which can be filled in up to 48 hours before your flight
Therefore, you must book your day 2 test before you arrive at the airport to take your flight to the UK