Requirements for travel to Portugal as far as I understand it.
1. Private paid for PCR test taken within 72 hours of flight departure time (Portugal rule)
2. Private PCR or LFT test taken within three days of return flight to UK. Porto airport does LFT tests with 30 mins results. If you travel out within three days of your outbound test (i.e. Test Thursday, Fri or Sat, return Sunday) you can use the outbound test for the return.(UK rules)
3. Private PCR test pre booked before leaving for Portugal to be taken before day 2 after arrival back in UK, proof of test retained to show at border control. (UK rules)
4.
https://portugalcleanandsafe.pt/en/passenger-locator-card, to be completed online after check in.
5.
https://www.gov.uk/provide-journey-contact-details-before-travel-uk, to be completed on line in the 48 hours before leaving for the UK. This is where you put the details of the test booked in step 3 above.
Temperature screening will take place on arrival in Portugal.