Brits coming back from Portugal could be forced to quarantine again by the end of the week unless it sees a "miracle drop", an expert has warned.
Paul Charles is CEO of travel consultancy The PC Agency which has correctly predicted the weekly government review for the past three weeks.
He said Portugal is on the brink of being in the "red zone" for the UK quarantine list after a sharp rise in coronavirus cases.
The warning came just days after the country was added to the UK government’s travel corridor.
"Portugal cases increase again, putting it on the brink of the red zone for #quarantine by Saturday morning," Mr Charles tweeted.
According to The PC Agency data, on Sunday Portugal recorded 19.4 cases per 100,000 people over the previous seven days.
The UK has said nations will be taken off the travel corridor list once this figure rises above 20.
Mr Charles told the Daily Mail : "It will need to see a miracle drop in case numbers by Thursday to avoid being added again to the Government's on-off quarantine list as it is quickly veering into the red zone."
He added that Portugal is a "victim of its own success in attracting so many tourists rapidly", with Skyscanner reporting a 2,000 percent increase in bookings from the UK since the travel corridor was added on August 22.
An estimated 75,000 Brits are either in the country or due to fly there.
Transport Secretary Grant Shapps has warned holidaymakers that quarantine rules can change rapidly.
On Thursday Switzerland, Jamaica and the Czech Republic were stripped from the "safe" list, meaning people arriving in the UK from those countries after 4am on Saturday now need self-isolate for two weeks.
France, Spain, Croatia, Trinidad and Tobago, Austria, Monaco, Malta, Turks & Caicos and Aruba, Andorra, Belgium and the Bahamas, Serbia and Luxembourg have also previously been removed.
Mr Shapps told Sky News: "Look there is a travel corridor list and I think it contains probably still about 55, 60 countries. It changes every week.
"They are there for a reason. However, when people travel at the moment when coronavirus is still a thing… just need to be aware that unfortunately things can change very quickly and, you know, if you go with your eyes open and you know that things can change, it won’t then come as so much as of a surprise."
He has previously said a range of factors are taken into account when the Joint Biosecurity Centre decided whether to add a country to the quarantine list.
They include estimated prevalence of Covid-19 in a country and the level and rate of change in the incidence of confirmed positive cases.
