- Coronavirus pandemic
People from the UK travelling to Portugal will have to quarantine for 14 days unless they can present proof they had been fully vaccinated a fortnight before their arrival.
The Portuguese government added the UK to the list of countries from which travellers must quarantine "at home or a place indicated by the health authorities".
The rules came into effect at midnight.
Germany also wants the European Union to restrict UK travellers.
Portugal is currently on the UK's amber list meaning arrivals back to the UK must take two tests and quarantine for 10 days.
The Portuguese government's new quarantine measures only apply to those travelling to mainland Portugal and not Madeira.
There are 19 flights listed as departing on Monday from UK airports to Portugal's mainland airports Lisbon, Faro and Porto.
The current travel list
The destinations added to the green list from 04:00 BST on 30 June are:
Europe: The Balearic Islands (which include Ibiza, Menorca, Majorca and Formentera), Malta and Madeira
Caribbean: Anguilla, Antigua and Barbuda, Barbados, British Virgin Islands, Cayman Islands, Dominica, Grenada, Montserrat and Turks and Caicos Islands
Other British Overseas Territories: Bermuda, British Antarctic Territory, British Indian Ocean Territory and Pitcairn
Six destinations will also be added to the government's red list on 30 June – the Dominican Republic, Eritrea, Haiti, Mongolia, Tunisia and Uganda
The Times reported German Chancellor Angela Merkel wants to designate the UK as a "country of concern" because the Delta variant of the coronavirus is so widespread.
The plans will be discussed by senior European and national officials on the EU's integrated political crisis response committee.
Mrs Merkel previously told Germany's parliament: "In our country, if you come from Great Britain, you have to go into quarantine – and that's not the case in every European country, and that's what I would like to see."
She is set to meet Prime Minister Boris Johnson at Chequers next week.
French President Emmanuel Macron has also talked about his concern at the spread of the variant.
Last week, Mr Macron said: "We should all be vigilant because the Delta variant is coming.
"We see that it affects people who have not yet been vaccinated or who have only had one dose, which means we have to be even faster in this vaccination campaign."
Currently, fully-vaccinated UK visitors to France can enter without quarantining.
- What are Portugal's new holiday quarantine rules?
- Things to check before booking a green list holiday
In Portugal, the legislation is in force until 11 July, but the Portuguese authorities stated it could be reviewed "at any time, depending on the evolution of the epidemiological situation".
Brazil, South Africa, India and Nepal were already on Portugal's quarantine list, but the exception for people who are vaccinated against Covid-19 to avoid isolating only applies to the UK.
For all countries on the list, an exception is also made for participants in specified sporting competitions being held in June and July.
What refund rights are there for holidays abroad?
With Covid still widespread in many countries, tourists will have to think carefully about their spending on holidays.
There is always a risk that a green-list country may move to the amber or red list. If this happens you will need to quarantine after your holiday – something that could be difficult for many people.
Operators do not have to refund you if you are unexpectedly forced to self-isolate on your return.
If the government announces that travel to a particular country is not advised, then airlines and travel companies are likely to cancel any pre-booked flights or holidays there.
In this case, you are entitled to a full refund and you can choose to receive that refund in cash.
Read more about your refund rights on holidays.
Are you planning a holiday this summer? Have your plans now had to change? Email [email protected].
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