The tests that must be taken within 3 days of return to the UK, must come from a test provider.
https://www.gov.uk/guidance/coronavirus-covid-19-testing-for-people-travelling-to-england
Googling your destination, you’ll find loads of labs or clinics doing this. Book in advance. We did in...
This.
In Ibiza three weeks ago, I got our hotel to print out a few bits, such as our locally done pcr test results.
It was made plain throughout by BA and the UK government rules, that only a third party lab test would suffice.