UK tourists have spent thousands of pounds on new flights and endured long drives in a race to get home before new coronavirus travel rules kicked in.
As of 04:00 BST on Saturday, travellers returning to the UK from Croatia, Austria and Trinidad and Tobago must quarantine for 14 days.
Children in families who did not return in time will miss the start of school in England, Wales and Northern Ireland.
But searches for flights to Portugal rose as it was put on the safe list.
Meanwhile, extra restrictions to stem the spread of Covid-19 have come into force in north-west England.
It comes as a further 18 deaths have been recorded in the UK, bringing the total number of people to have died within 28 days of testing positive for coronavirus to 41,423.
The quarantine measures for Croatia, Austria and Trinidad and Tobago have been imposed because of a spike in coronavirus cases in those countries, the UK government has said.
As of 21 August, the UK recorded 21.2 coronavirus cases per 100,000 people over the last fortnight, according to the European Centre for Disease Prevention and Control.
In comparison, Croatia had 47.2 cases per 100,000, Austria had 33.0 and Portugal 28.5.
There were about 17,000 British tourists in Croatia on Friday, according to the country's national tourist board.
On Friday evening, British Airways flights arriving from the Croatian city of Dubrovnik and the capital Zagreb at London's Heathrow airport were among the last to reach the UK before the deadline.
Jane Grist, from Walton-on-Thames, Surrey, said she was "livid" because the rule change meant her two sons would have to miss the first week of school after they return from the Croatian city of Sibenik, on 27 August.
"We've been focusing on the return to school as a return to normality," she said.
"Now we've got to explain [to our youngest son] he won't be able to go back at the same time as all of his friends."
Ms Grist said the holiday was "the one thing we have been looking forward to" after she was made redundant last year - and now it has been "spoilt".
Frano Matušić, Croatia's State Secretary for Tourism, said his country was "really disappointed" by the new quarantine rules and urged the UK government to reverse its decision.
"We think that this decision was not fair because we think that Croatia is a really safe destination," he told Sky News.
Another Friday, another country in Europe where hundreds of British tourists have frantically had to figure out ways to head home early.
The airline authorities here in Split put on two extra flights on Friday to cope with the sudden demand. There were at least 500 passengers on board both aircraft. All were British travellers who booked last minute.
"It beggars belief. Why was there such short notice for us to leave?" Karen, an English teacher, tells me. She'd just begun a week in Split and was in the middle of booking a ferry to Italy to get out of the country by the evening, because she said the UK flights had sold out.
In the beautiful medieval town of Sibernik, a group of eight friends from Nottingham Trent University had given up efforts to get back early. Instead they drank beers in a harbour-side cafe.
Lou, 20, said: "We tried to get something, but everything was too expensive."
Her friend Amber added: "It's upsetting because we planned this trip carefully, and quarantine means we can't go back to part-time work for two weeks, which sucks because it helped towards my university studies."
Neil Warnes, 59, from Margate, was on holiday with his wife and two teenage children in an Alpine village in Austria when he heard the news on Thursday evening.
The family spent about £2,000 to cut their holiday short by one day, in order to get home before the quarantine rules came into effect. They left Seefeld - a town with "hardly any people there" - at 02:00 on Friday to get to Munich airport, for an early morning flight to Heathrow.
"As our car was parked at Gatwick, another cab journey was needed and we finally arrived home in Kent at midday," Mr Warnes said.
"Austria appeared to be adhering to all social distancing measures and hand sanitation stations were in all the shops. Our small hotel had three alone on the ground floor.
"With this in mind we were so surprised when the government restrictions were put in place as Austria have had a historically low level since March. There didn't really appear to be any problems at all," he added.
'I wish we'd stayed at home'
Another traveller, Cristiano Torti, 41, paid about £1,500 to fly his wife and two children back to the UK six days earlier than planned.
He said they had lost about £500 of the original return flight bookings, but it would have been "very difficult" to quarantine with his young children as he and his wife both work from home.
Mr Torti, a developer from Oxfordshire, said that his eldest child would have missed some of the new school term had the family not returned in time.
"We've lost a lot of of money, between the accommodation, the flights, and the knock-on effects: the car hire, the airport parking. I kind of wish we'd stayed home, despite the miserable British weather," he said.
Meanwhile, Google search data showed a significant rise in searches for the term "flights to Portugal" by UK users at about 18:00 BST on Thursday; with a smaller spike at 07:00 BST on Friday morning.
Several EasyJet flights from London airports to Portugal were listed as unavailable for Saturday and Sunday, while airlines such as Jet2 laid on extra seats to Faro from Monday across the UK.
Travel expert Simon Calder tweeted that the cost of flights from Manchester to Faro on Saturday morning had risen from £50 to £98 in 30 minutes.
People who do not self-isolate when required can be fined up to £1,000 in England, Wales, and Northern Ireland. In Scotland the fine is £480, and up to £5,000 for persistent offenders.
The UK introduced the compulsory 14-day quarantine for arrivals from overseas in early June.
But the following month, the four UK nations unveiled lists of "travel corridors", detailing countries that were exempt from the rule.
Since then it has periodically updated that list, adding and removing countries based on their coronavirus infection rates and how they compare with the UK's.
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