At 4:00 a.m.BST on Saturday, those returning to the UK from Croatia, Austria and Trinidad and Tobago will be quarantined for 14 days.
Children from families who have returned on time will miss the start of school in England, Wales and Northern Ireland.
But the search for flights to Portugal has increased as it has been included in the list.
Meanwhile, more restrictions have come into effect to stop Covid-19 in North West England.
It occurs when 18 more deaths have been reported in the UK, bringing the total number of others who have died within 28 days of the positive coronavirus test to 41,423.
Quarantine measures were imposed for Croatia, Austria and Trinidad and Tobago due to an increase in coronavirus cases in those countries, the British said.
As of 21 August, the UK had recorded 21.2 cases of coronavirus in line with another 100,000 people in the past fortnight, according to the European Centre for Disease Prevention and Control.
By comparison, Croatia obtained 47.2, consisting of 100,000, Austria 33.0 and Portugal 28.5.
Nearly 17,000 British tourists flocked to Croatia on Friday, to the country’s national tourist office.
On Friday night, British Airways flights from the Croatian city of Dubrovnik and the capital Zagreb to London Heathrow Airport were among the last to succeed in the UK before the deadline.
Jane Grist, of Walton-on-Thames, Surrey, said she was “furious” because replacing the rule meant that her two sons would have to miss the first week of school after returning from the Croatian city of Sibenik on 27 August.
“Our goal was to go back to school as a return to normal,” he said.
“Now we have to [our youngest son] who won’t be able to come back at the same time as all his friends.”
Ms. Grist said the vacation was “the only thing we were looking for” after she fired last year, and now she’s “spoiled.”
Croatia’s Secretary of State for Tourism Frano Matu-i said his country “really disappointed” by new quarantine regulations and suggested the British government oppose its decision.
“We believe this resolution was not fair because we believe Croatia is a safe destination,” he told Sky News.
Another Friday, a European country where many British tourists desperately had to look for tactics to get home early.
The aviation government here in Split installed two more flights on Friday to meet demand.There were at least 500 passengers on both planes. They were all British travelers who had booked at the last minute.
“It’s pure faith. Why is there so little time for us to leave?” Karen, an English teacher, tells me. She had just started a week in Split and was booking a ferry to Italy to leave the country for the night, having said that British flights were sold out.
In the charming medieval town of Sibernik, an organization of eight friends from the University of Nottingham Trent had given up returning early and instead drank beers at a harbour café.
Lou, 20, said, “We’re trying to get something, but all too expensive.”
Her friend Amber added: “It’s provocative because we planned this carefully, and quarantine means we can’t repaint part-time for two weeks, which sucks because it helped my college studies.”
Neil Warnes, 59, from Margate, on holiday with his wife and two teenagers in an Alpine village in Austria when he heard the news on Thursday night.
The family circle spent about 2000 euros to shorten their one-day vacation, in order to return home before quarantine rules came into force.They left Seefeld, a town where “there were almost no people,” on Friday at 02.: 00 to get to Munich airport, to take an early morning flight to Heathrow.
“Because our car was parked in Gatwick, it took another taxi ride and yet we got home to Kent at noon,” Warnes said.
Austria to adhere to all measures of social estating and hand disinfection stations were in all shops.Our small hotel had 3 on the floor.
“With this in mind, we were very surprised when government restrictions were implemented, as Austria has been at a traditionally low point since March.There doesn’t seem to be any problems,” he added.
Another traveller, Cristiano Torti, 41, paid about 1,500 euros to bring his wife and two young men to the UK six days earlier than planned.
He claimed that they had lost around 500 euros in the original flight bookings, but that it would have been “very difficult” to quarantine their young children, as he and his wife paint from home.
Torti, an Oxfordshire developer, said his eldest son would have missed a component of the new school term if the circle of relatives had not returned in time.
“We lost a lot of money, between accommodation, flights and domino effects: car rental, airport parking.I would have liked to stay home, despite the bad British weather.”he said.
Meanwhile, Google Search Knowledge showed a significant increase in searches for the term “flights to Portugal” through British users around 18:00 BST on Thursday; with a smaller peak at 07:00 BST on Friday morning.
Several EasyJet flights between London and Portugal airports have been indexed as unavailable for Saturday and Sunday, while airlines like Jet2 have put more seats to Faro since Monday across the UK.
Travel expert Simon Calder tweeted that the fare for flights from Manchester to Faro on Saturday morning had 50 to 98 euros in 30 minutes.
People who are not isolated when they can be fined up to EUR 1000 in England, Wales and Northern Ireland, in Scotland the fine is EUR 480 and up to EUR 5,000 for repeat offenders.
The United Kingdom imposed mandatory 14-day quarantine for arrivals in early June.
But the following month, the Four British countries revealed lists of “travel corridors”, detailing the countries that were exempt from the rule.
Since then, it has updated this list, adding and cutting countries based on their coronavirus infection rates and their comparison with the UK.
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