Under plans being decided by ministers over the next 24 hours, some travellers will be put on buses and driven directly to isolation centres.
But ministers are not ruling out extending the plan to all passengers and countries to defend against the risk of another mutation that nobody yet knows about.
The Prime Minister spoke of the need to defend the “immense effort by the NHS” in vaccinating the millions of elderly people, key workers and those most vulnerable to the disease.
“We have to realise that there is at least the theoretical risk that there is a new variant, a vaccine-busting variant coming in,” he said. “So we will need to keep that under control.”
The dramatic move to defend the UK from more deadly mutations of Covid-19 is by far the toughest border measure yet.
The key question to be settled by ministers, who are in meetings with scientists today, is whether to target the measure only at passengers who have visited countries such as Brazil and South Africa or whether to target passengers from other countries.
Hawks in the Cabinet, including Health Secretary Matt Hancock, say mutations could exist in countries that lack advanced genome monitoring without anybody realising the threat exists until it arrives.
The most severe option is to insist on quarantine for all passengers, which would require thousands of hotel rooms and monitoring. Passengers will have to pay their hotel bills and will also have to take a negative test for coronavirus before they are released.
Speaking during a visit to a vaccination centre at Barnet Football Club, Mr Johnson said: “If we’re going to make that effort [of mass vaccinations], which we are, we want to make sure we protect this country against reinfection from abroad. So that idea of looking at hotels is certainly one thing we’re actively now working on.”
Mr Johnson continued: “At the moment the UK already has one of the tightest regimes in the world. Don’t forget everybody when you’re coming into the UK, that you have to have a test 72 hours before you fly, you have to have a passenger locater form, the airline will kick you off if you don’t produce either of those. And then they test your passenger locater form. And then of course you need to quarantine for 10 days — five days with another negative test.”
Some 6.3 million people have now been vaccinated in Britain.
Mr Hancock signalled his backing for tough measures when he said yesterday: “The new variant I really worry about is the one that is out there that hasn’t been spotted.
“There’s probably those elsewhere that simply haven’t been picked up because the country doesn’t have that genomic sequencing service.”
There are 77 known cases of the South African variant in the UK and nine of the Brazilian. All the cases of the South African variant have been linked to travel. He said that Brazil and South Africa spotted the variants because they had “decent-sized” genomic sequencing programmes but other countries were less well covered.
Yesterday, the Health Secretary took a swipe at influencers and celebrities as he criticised people travelling overseas amid the pandemic. Speaking on the BBC’s Andrew Marr Show, Mr Hancock said: “International travel, right now, should not be happening unless it’s absolutely necessary. No parties in Paris or weekends in Dubai. That is not on and in most cases it’s against the law.”
Number of known cases of the South African variant in Britain.
There are nine Brazilian
The comments came after a number of social media influencers were criticised over trips to Dubai that they documented on Instagram.
His reference to “parties in Paris” comes after model Kate Moss spent her 47th birthday in the French capital with her boyfriend Nikolai von Bismarck and daughter Lila Grace.
Sources told The Mail on Sunday that Moss had to travel for work and had been forced to break off a Caribbean holiday to do so.
In other developments, Labour leader Sir Keir Starmer is self-isolating for the third time after he came into contact with someone who has tested positive for coronavirus.
Sir Keir wrote on Twitter: “This morning I was notified that I must self-isolate after coming into contact with someone who has tested positive for Covid-19.
“I have no symptoms and will be working from home until next Monday.”