UK nationals resident in Portugal after the end of 31/12/2020 are asked to exchange their current EU residence document for one that confirms their status as a resident under the Withdrawal agreement.
If you were living in Portugal before 1/1/2021 but have not registered as resident, you will need to keep evidence that you arrived intending to live here. The process for this has not yet been formalised by the Portuguese government.
UK nationals are allowed in the Schengen Area for stays of up to 90 days in a rolling 180-day period without requiring a visa.
From 1 January 2021 permission is required from the Portuguese Border and Immigration services (SEF) to stay longer than 90 days.
If you are in the UK and want to apply for Portuguese residency you will need to make an appointment to apply for a Visa . Visas are issued by VSF globalapply here
SEF have confirmed that if you arrived in Portugal before the31 December 2020 and you are not resident or don’t intend to become resident, and you are still in Portugal due to the COVID -19 travel restrictions, you do not need a visa or further authorisation to stay in Portugal longer than 90 days.
As the right to free movement was being exercised when you arrived, and you are not subject to immigration control.
The Secretary of State for Tax affairs issued the order 514/2020 for the requirement for UK nationals with Portuguese tax numbers to appoint a Fiscal Representative. Due to the Covid 19 pandemic this has been extended until 30 June 2021. There is a penalty for non-appointment that may vary between €150 and €3,750.