2 days before Departure from another country, to the UK - PCR tests

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Someone I know is going to either fly from Portugal, Spain or Gibraltar, into the UK. In about 1 week's time.

If the plane leaves at 2pm, at what point should the PCR test be done please?
The person has asked for my help because he has googled out where he is, and cant find the exact answer.

Thanks.

www.gov.uk/guidance/coronavirus-covid-19-testing-for-people-travelling-to-england

Assuming england - details here quite clear (similar pages apply for Scotland, Wales and NI)

It doesn't have to be a PCR. Antigen/rapid lateral flow is suitable.

Thank you. Just what he needed and wasnt able to find.