The British Government has announced a mandatory 14-day coronavirus quarantine for all incoming travellers from overseas.
The move, which does not come into force until June 8, has angered airlines who fear it will devastate the already frail industry.
Under the rules, announced by Home Secretary Priti Patel, all international arrivals — including British citizens — will be required to self-isolate for 14 days and provide details of where they will be staying to the authorities.
"Now we are past the peak of this virus, we must take steps to guard against imported cases triggering a resurgence of this deadly disease," Ms Patel said during the Downing Street daily press conference.
"We are introducing these new measures now to keep the transmission rate down and prevent a devastating second wave.
"Arrivals will be required to travel directly from their port or airport of arrival, preferably by car, to an address where they must then self-isolate for a fortnight."
She said those who breached the quarantine in England could be fined 1,000 pounds (A$1,863), and that spot checks would be carried out by health and border officials.
Those whose accommodation does not allow for self-isolation will be set up in facilities provided by the government, but at a cost to the traveller.
The quarantine measures will not apply to those arriving from the Republic of Ireland, and there are also exemptions for freight drivers, medical professionals and seasonal agricultural workers.
Critics have questioned why the measures have been introduced so late, with Britain only enforcing quarantine on travellers coming from China and northern Italy at the start of the coronavirus pandemic.
Airline bosses said the measures would have severe repercussions, with Michael O'Leary, chief executive of low-cost carrier Ryanair, saying they would be "unenforceable and unpoliceable" and would be ignored.
"Introducing a quarantine at this stage makes no sense and will mean very limited international aviation at best," Tim Alderslade, chief executive of industry body Airlines UK, said.
"It is just about the worst thing [the] government could do if their aim is to restart the economy."
The Government said the quarantine measures will be reviewed every three weeks.