Families wept as they were reunited at London's Heathrow Airport on Monday, with fully vaccinated passengers arriving in England from the US and EU no longer required to quarantine.
Tight controls on foreign travel have been in place in Britain for over a year, leaving families separated during the coronavirus pandemic.
But restrictions in England and Scotland eased on Monday, leading to emotional scenes at Heathrow, Britain's busiest hub.
"We're feeling very excited, almost overexcited," said Michael Blake, 71, as he waited with wife Sue to see their son Eliot and 8-year-old grandson for the first time in 18 months.
"It's been such a big chunk of (our grandson's) life that he hasn't seen any grandparents," Sue told AFP, as she waited for the 6:20 am (0520 GMT) flight from New York.
On sight of her son, Sue ducked under the barrier at arrivals and embraced her grandson, wiping tears from her eyes.
Her family were one of the first to take advantage of the new policy, which came into force in England and Scotland from 4:00 am.
Under the new rules, people fully jabbed with a vaccine approved by the US Food and Drug Administration or the European Medicines Agency can travel from any country on the British government's "amber" traffic light list without having to self-isolate at home for 10 days.
They still need to do a pre-departure test and take another test on day two after arriving.
- 'Disaster' warning -
Separate rules will continue to apply for those arriving from France due to the government's concern over the "persistent presence" of the Beta variant, which is believed to be more resistant to vaccines.
Those who are not fully vaccinated will still have to quarantine on arrival.
Britain is in the midst of another wave of the virus due to the Delta variant, although case numbers appear to be stabilizing, while its vaccine drive has seen more than 70 percent of adults fully jabbed.
While England and Scotland have loosened their quarantine requirements, the previous rules still apply in Wales and Northern Ireland.
Embattled airline bosses called the rule changes a positive step but said industry recovery efforts were being hampered by continued international restrictions.
Heathrow Airport chief executive John Holland-Kaye told BBC radio that the industry would not "get back to normal" until the US opens its borders to people travelling from Britain.
Industry leaders also warned the government against introducing another category to its traffic light list, designed to warn travelers of the possibility that countries with rising cases could be put onto the red list at short notice.
"It would be a disaster to bring in an amber watchlist on top of the amber list, the green list, the red list," Paul Charles, chief executive of travel consultancy The PC Agency, told ITV.
"At the moment the system in the UK is choking off recovery, and it's not helping the sector because there's no confidence to book because people are worried about places changing at short notice anyway," he added.
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