This week, Wales and Scotland both added Portugal to their quarantines lists but England and Northern Ireland decided not to revoke Portugal’s travel corridor.

Scotland and Wales’s quarantine requirements for Greece have also now diverged from England, with the Scottish government requiring all arrivals from Greece to self-isolate for 14 days, while the Welsh government is doing the same for six Greek islands.

“I realise things are confusing for people,” Shapps told the BBC. “The way the law is drafted is different in each country.”

Shapps added that governments across the four nations all received the same data about the spread of Covid-19 in different countries from the Joint Biosecurity Centre (JBC).

“Scotland took the decision [on Greece] before looking at the Joint Biosecurity data because they had particular concerns about people coming back from Greece,” said Shapps.

The transport secretary also stressed that quarantine decisions were not just made on the number of Covid-19 cases per 100,000 people.

“That’s a useful benchmark but it’s not the only thing the Joint Biosecurity Centre looks at,” he said. “Another thing they look at is test positivity – the percentage of those tests that turn out to be positive.

“If you test more people, then the number of positives is going to be more. You also look at how it’s being treated and how fast it’s moving. The level per 100,000 is only a rule of thumb.”

Shapps admitted that Portugal was “borderline” this week in terms of losing its travel corridor with England.

Even though Portugal’s number of cases per 100,000 people has risen beyond the benchmark of 20 over a seven-day period, Shapps said the country did not “justify quarantine” this week because other Covid indicators in Portugal have been going down at the same time.

“It can change very quickly,” Shapps warned. “I have every sympathy for people who become stranded.”

Meanwhile Wales’ health minister Vaughan Gething defended the country’s quarantine moves this week because they were “about keeping Wales safe”.

He added: “I won’t wait until there’s a much larger infection rate from these parts of Europe before taking action. There’s a rising rate of infection from these particular [Greek] islands.”