On Tuesday all international arrivals to the UK will need to take a pre-departure Covid-19 test to tackle the new Omicron variant.
The change comes into force from 04:00 GMT, with travellers over the age of 12 having to submit evidence of a negative lateral flow or PCR test that has been taken a maximum of 48 hours before the departure to the UK.
The news dismayed the travel industry, but for travellers about to leave the UK the extra cost, confusion and inconvenience about getting tested before returning now overshadows their trips.
Some are even considering cancelling because there is no guarantee the rules won't change yet again.
Matthew O'Toole has no intention of cancelling his one-day visit to Portugal - but he's still not entirely sure of the rules, nor the likely disruption and extra costs.
He's collecting his young daughters to spend Christmas in the UK, with the plan being that the girls travel from Spain with their mother across the border to Faro airport.
He told the BBC: "The girls live near Portuguese border, so it's easier for me to go from Gatwick and fly to Faro. I go to the airport, hang about, the girls get dropped off with me, we go back with them same day.
"I haven't had them here since Christmas 2019. I saw them one week in August this year," he said.
This time he's planning to collect them on 21 December and return them on 2 January. Mr O'Toole said that while a review of the rules is possible in the next couple of weeks, that is no help for his planning.
"We're up in the air on the tests. I have to test to go to Portugal and then we all have to test to get back into the UK. I have to do tests that I am fit to fly even though [I return] on the same day.
"There's also talk of a test to cross the border from Portugal to Spain. It's going to cost a fortune, I just wish there was more guidance," Mr O'Toole said.
Another family facing a possible big increase in costs - which could scupper their holiday plans - is Annette Mitchell and her children.
She's booked a holiday to New York with her teenagers, departing on 6 January.
Annette has already book pre-Covid tests ahead of departure at a cost of £105, she told the BBC. Then there was the introduction of tests in arrival in the UK, which are booked and paid for at Heathrow Airport - another £205.
"Already the trip is expensive without added costs," she said. "Now we are being told to test before we return to the UK. The only tests in the US are a cost of $200 each - that's what it says on the Virgin Atlantic website.
"So a total of $600 (£453). That's another holiday," Annette said.
She's wondering if they can now afford to go, something that's not only upsetting her, but also the children. "It's so stressful because we can't afford paying another $200 per person."
Duncan Binnie is another person who's festive plans have been thrown into disarray. A Briton, he now lives just outside Paris and plans to return to the UK to see his children over Christmas.
He told the BBC: "They're being very careful in France - I would almost call it panicking. We've done the vaccinations, we're home working, isolating, done the lockdowns.
"I was due to come home later in the month but I'm moving all my travel forward." He fears France could impose tougher restrictions along with the UK.
"I haven't seen my two children in two-and-a-half years. The last time I saw my daughter was for her 18th birthday and now she's 20 years old," Mr Binnie said.
To protect himself ahead of his trip he's particularly careful. "I've not been to office in over a week and stayed off transport.
"I've had to pay for testing, as in France if you're symptom-free you must pay. Whereas, if you have symptoms, it's free."
He's worried about being stuck in the UK if tougher rules are introduced in France. "But I need to see my children, and I don't mind having to pay extra to do that."
He added: "I feel like we're getting penalised when we shouldn't be. I've made a lot of sacrifices over the past two years; I just want some normality."
BBC