Boris Johnson has hinted that some holiday destinations could be removed from the UK green list.
There are currently twelve countries, including Portugal and Israel, to which people cannot travel without having to put on quarantine when they return home.
The government is expected to release an update on its international travel standards on Thursday.
Asked if more countries would be added to the green list, Johnson said he had to be “prudent.”
He noted that it was only mentioned that countries increased a level of Covid risk, not that they decreased.
“We must continue to put countries on the red list, on the amber list, when necessary,” the prime minister said.
“We will have no hesitation in changing countries from the green list, to the amber list, to the red list, if we have to do it”
He added: “The priority is to continue with the implementation of the vaccine, to protect the people of this country.”
Travelers returning to Britain from an amber site must be quarantined at home for 10 days and take a pre-departure test and two post-arrival tests.
People arriving from a red list country must quarantine in a government-approved hotel.
Currently, the red list consists of 43 countries from which arrivals are considered to be at high risk of importing Covid.