As a resident in Portugal, you have the right to access state healthcare on the same basis as Portuguese citizens. It is especailly important at the moment to register with the Portuguese national healthcare system (SNS), to ensure you are contacted to receive your Covid-19 vaccination. How do you do it?
To aqcuire your health sysytem number (Numero de Utente de Saude) you need to visit your local Centro de Saude (health centre), with your passport, NIF (fiscal number) and residency document/card. It is not essential to have a social security number but if you have one, take it. Just ask to register, and they will ask for the afore mentioned documents, plus your email address and a Portuguese mobile number.
If you have a UK state pension, ask the NHS Overseas Healthcare Team for an S1 form and register it at a Social Security District Centre in Portugal. You will need to present a copy of the S1 form when requesting your health system registration.
Once they have entered your infomation on the system, this only takes a few minutes, you will be given a document confirming your healthcare details.
NHS Overseas Healthcare Team: https://www.nhsbsa.nhs.uk/contact-us/overseas-healthcare-services-contact-us