Transport Secretary Grant Shapps confirmed the move, which comes after a steady rise in coronavirus cases, on Thursday evening.
Hungary, French Polynesia and Reunion were also added to the list. Anyone arriving in England from any of these countries after 4am on Saturday will have to self-isolate for 14 days.
People arriving in Scotland and Wales from Portugal must also isolate, but it is still exempt from Northern Ireland’s rules.
The UK’s quarantine list has been growing over the past few weeks, as second spikes of Covid-19 crop up across Europe.
Why was Portugal re-added to the quarantine list?
The new restrictions apply to mainland Portugal and its smaller islands but do not include Madeira and the Azores, where infections remain low.
The Department for Transport said: “The Government has made consistently clear it will take decisive action if necessary to contain the virus, and data from the Joint Biosecurity Centre and Public Health England has indicated a significant change in both the level and pace of confirmed cases of coronavirus in Portugal, Hungary, French Polynesia and Reunion.”
The Foreign and Commonwealth Office (FCO) is now advising against all but essential travel to mainland Portugal. This means you will not be able to get travel insurance if you decide to go.
Where am I allowed to go on holiday?
Here is the full list of countries currently exempt from UK quarantine rules:
Akrotiri and Dhekelia Anguilla Antigua and Barbuda Australia The Azores Barbados Bermuda Bonaire, St Eustatius and Saba British Antarctic Territory British Indian Ocean Territory British Virgin Islands Brunei Cayman Islands The Channel Islands Cuba (added 4am, 29 August 2020 – if you arrived in England from Cuba before 4am 29 August you will need to self-isolate) Curaçao Cyprus Denmark Dominica Estonia Falkland Islands Faroe Islands Fiji Finland Gibraltar Germany Greece (except the islands of Crete, Lesvos, Mykonos, Santorini, Serifos, Tinos and Zakynthos – if you arrive in England from any of these islands after 4am 9 September 2020 you will