Denmark, Slovakia and Iceland have been added to England and Wales’ travel quarantine lists – meaning travellers returning from 4am on Saturday will have to self-isolate for two weeks.
The Caribbean island of Curacao has also been added to the lists.
The government’s “red list” is aimed at stopping coronavirus spreading from countries with high infection rates.
Anyone who fails to quarantine after returning from these countries – apart from a small list of exemptions – faces a fine starting at £1,000.
No countries have been removed from the red list this week, Transport Secretary Grant Shapps confirmed.
The UK government first announced the changes for England, before Wales said it would follow suit.
The government makes its quarantine decisions based on – among other things – whether a country’s weekly infection rate is above 20 cases per 100,000 people.
The latest figures show Denmark has a weekly infection rate of 45.3 per 100,000, surpassing the UK’s 38.6 per 100,000.
Slovakia is at 24.6 per 100,000, while Iceland is at 50.7.
Public Health England officials have been contacting people to check if they are following the rules and if they fail to get a response passenger details are passed to the police.
Police have revealed that two people in Bolton – which has the highest infection rate in England – have been hit with £1,000 fines after returning from Spain and Amsterdam.
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Paul Charles, chief executive of travel consultancy The PC Agency, said: “It’s sad to see the list of countries growing on the quarantine list in line with the resurgence of COVID-19 in several parts of the world.
“It now makes even more sense for traveller testing to be introduced as soon as possible, reducing quarantine times and enabling economies to get going again.
“A co-ordinated, global programme, combining testing with short quarantine periods if necessary, would help protect lives and livelihoods.”