The UK government imposed an emergency ban on flights and ships to England from Denmark to try to stop the spread of a new strain of coronavirus linked to mink farms.
The WHO said on Friday that six European countries had detected the new mutation, sparking fears it might override the effectiveness of a Covid-19 vaccine.
Italy, the Netherlands, Spain, Sweden and the US have also discovered the coronavirus in mink.
Stricter measures to curb the spread led to a ban on passenger planes from Denmark and on ships docking in English ports on Saturday.
On Sunday, the ban was extended to all non-UK freight drivers who have travelled through Denmark in the past 14 days and all UK citizens wishing to enter England were told they must isolate for 14 days.
Foreign Secretary Dominic Raab said the ban was the “right decision”.
“The concern is that you see a mutated version of the coronavirus and that if it spread, it would undermine our ability to make an effective vaccine,” he told Sky News on Sunday.
“We need to look very carefully at the science.”
But policing of the measures is being questioned because the curbs rely on people abiding by isolation rules and not using public transport.
The UK Home Office said it was “stepping up Border Force presence” to ensure that those arriving in the UK from Denmark were complying with the new restrictions.
Dash to test and trace Denmark returnees
Denmark, the biggest producer of mink fur in the world, is culling 17 million of the animals after the animals infected some workers on farms.
“Given the significant unknowns regarding the new mutation of Covid-19 originating in Denmark, we have moved quickly to protect our citizens and prevent the spread of the virus to the UK,” the Department of Transport said.
“The UK government is working closely with international partners to understand the changes in the virus that have been reported in Denmark and we are conducting a programme of further research here in the UK to inform our risk assessments.”
Health officials are trying to test and trace at least 6,000 people who flew into the UK from Denmark in the past fortnight.
On Saturday, the UK recorded 413 deaths from the virus and the number of people testing positive rose by 24,957, a daily increase of 1,670.
Amid the surging cases, France, Germany and England announced nationwide lockdowns for at least the next month, which are almost as strict as the restrictions in March and April.
Here is a list of the rules for the second lockdown in England.
Portugal has imposed a partial lockdown and Spain and Italy are tightening restrictions.
On Sunday, the number of confirmed coronavirus cases in Germany increased by 16,017 to 658,505, data from the Robert Koch Institute for infectious diseases showed, with the reported death toll rising by 63 to 11,289.
Anti-lockdown sentiment spreads
It followed a night of further violent protests against coronavirus restrictions in Leipzig with demonstrations an increasingly prevalent display of anti-lockdown sentiment across Europe.
Thousands of protesters, who did not wear masks or observe social distance, showed the “height of irresponsibility and egotism”, Justice Minister Christine Lambrecht said.
“Such a situation cannot be allowed to happen again in the midst of a pandemic.”
France reported almost 90,000 new daily cases on Saturday – a record high for the third day in a row.
"The second wave has arrived here brutally, violently,” French Prime Minister Jean Castex tweeted.
France said this week that it was using 4,089 of its 6,400 intensive care beds.
