Passengers arriving at London’s Heathrow Airport were escorted by security guards to buses that took them to nearby hotels.
Some of the travelers said they had tried and failed to make it to Britain before Monday to avoid the quarantine.
AdVisiting a London vaccination center on Monday, Prime Minister Boris Johnson praised the “unbelievable effort” by scientists, medics, pharmacists, members of the military and volunteers that had achieved Europe’s fastest vaccine rollout.
Health Secretary Matt Hancock said the vaccination drive is now being extended to people over 65 and those with underlying health conditions.
Britain has had Europe’s worst coronavirus outbreak, with more than 117,000 deaths, though Infections and deaths are now falling steadily after more than a month of national lockdown.