Family holidays to Portugal have been thrown into doubt as it emerged all children aged 12 and over will have to be vaccinated or face quarantine on arrival.

The Portuguese government added the UK to a list of countries which requires travellers to provide proof of being fully vaccinated or to quarantine for 14 days “at home or a place indicated by the health authorities”. Only children under 12 are exempt.

On Monday, Spain also introduced new restrictions on UK travellers after demands by Angela Merkel, the German chancellor, for EU states to follow her country’s example and impose quarantine on UK citizens. The restrictions aim to combat the spread of the delta variant and apply even if travellers are vaccinated.

Mrs Merkel wants an “emergency brake” so tougher restrictions can be imposed on the UK. She has been backed by Emmanuel Macron, the French president, who wants EU states to take a common position on the UK to prevent a surge of the delta variant.

The Portuguese move falls short of Mrs Merkel’s demands but still means any double vaccinated parents travelling with teenagers will have to isolate for 14 days under the new regulations. They will remain in force until at least July 11.

Madeira, which joins the UK’s green list on Tuesday, is exempt from the requirement that applies to Portugal’s mainland. Portugal is on the UK’s amber list, requiring passengers to quarantine on their return, even if fully vaccinated.

TUI, the UK’s biggest travel operator, said it was likely to cancel flights to Portugal but would continue with its holiday programme to Madeira. One Lisbon-based British owner of a holiday business feared  it would “kill off” British bookings.

On Monday there were 19 flights listed as departing from UK airports to Portugal’s mainland airports: Lisbon, Faro and Porto.

Pedro Sanchez, the Spanish prime minister, announced on Monday that UK travellers will either need to prove they are fully vaccinated, or provide a negative PCR test on arrival if they are aged 12 or over.

The change, which comes into effect later this week, follows on from an announcement in May by Spain that it was lifting all restrictions for British visitors, who represent the country’s biggest single foreign tourism market. 

It will have the biggest impact on the Balearic islands of Ibiza, Mallorca and Menorca which join the UK’s green list allowing for quarantine-free travel from Wednesday.

Malta imposed 14-day quarantine on unvaccinated Britons and children over 12 just hours after being added to the UK green list, while Italy has demanded Britons self-isolate for five days and provide a negative Covid test.

Meanwhile, Hong Kong announced it was banning all passenger flights from the UK from July 1 after adding the UK to its “extremely high-risk” group of countries. A government statement said cases imported from the UK “involving variant virus strains” had been “persistently” detected in the past few days.

A Downing Street spokesperson said the choice of restrictions were a “matter for individual countries” but accepted those which had not achieved the UK’s high vaccination rate “may wish to be more cautious”.

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Boris Johnson is due to meet Mrs Merkel on Friday at Chequers where he is expected to press for agreed protocols that could safely open up foreign travel.

The Government has signalled that fully vaccinated Britons will be able to travel to amber list countries without having to quarantine on their return “later in the summer,” with early August more likely than mid-July.

EU officials disclosed that negotiations were “going well” for the UK to participate in the EU’s green certification scheme, which allows people to travel freely across the continent with proof of vaccinations or test results.

Despite Mrs Merkel’s hardline stance, a commission spokesperson said: “The situation that applies to the UK at present is travellers who are fully vaccinated… should be allowed by member states to arrive into the EU. We expect member states to apply this recommendation fully.”