People planning to go abroad have been warned "no travel is risk-free", and they should factor in potentially having to self-isolate for 14 days upon their return.
Quarantine restrictions have been reintroduced for people entering the UK from France, from 04:00 BST on 15 August, directly affecting about 160,000 British tourists.
Travellers arriving from several other countries, including Spain, also have told to self-isolate on arrival.
How does the government decide which countries go on the quarantine list?
The decision is triggered when a country's rate of infection exceeds 20 cases per 100,000 people over seven days. Transport Secretary Grant Shapps told BBC Breakfast France had reached 20.5.
The Joint Biosecurity Centre (JBS) - set up by the government to monitor coronavirus - advises which countries should be on the quarantine list, and which should be exempt.
- an estimate of the proportion of the population that is currently infectious
- trends in incidence and deaths
- transmission status
- information on a country's testing capacity
Why did the quarantine rules change for France and Spain?
In June, a two-week quarantine was brought in for most people entering the UK from overseas.
In July, the government published a list of more than 50 countries exempted from the rules because of their lower coronavirus rates.
But quarantine restrictions have been reapplied to several countries since then:
- 15 August - France, Netherlands, Malta, Monaco, Turks & Caicos, Aruba
- 8 August- Belgium, Andorra, Bahamas
- 31 July - Luxembourg
- 27 July - Spain
The decision that travellers from France and other countries would have to go into quarantine followed a "significant change" in the risk of contracting Covid-19, the Department for Transport said.
It added that there had been a 66% increase in newly-reported cases per 100,000 people in France since last Friday.
Spain was removed from the list of exempt countries in July following "a significant change... in both the level and pace" of coronavirus cases, the UK government said.
The Covid-19 infection rate in Spain has continued to rise, and in the first two weeks of August saw 110 cases per 100,000, according to the European Centre for Disease Prevention and Control, while the UK's rate is 17.3.
In Luxembourg and Belgium, which have been removed from the list, two-week rates per 100,000 people stand at 122.5 and 58.7 respectively.
The list is kept under constant review, and the government says it ''will not hesitate'' to remove more countries if conditions worsen.
Where can I go without quarantining when I get back?
Travellers are exempt from quarantine if they arrive in England, Wales and Northern Ireland from countries that - according to the government - pose a "reduced risk" from coronavirus.
Brunei and Malaysia were added to the exemptions list at 04:00 BST on 11 August.
It also includes:
Antigua and Barbuda, Australia, Austria, Barbados, BES Islands, Croatia, Curaçao, Cyprus, Czech Republic, Denmark, Dominica, Estonia, Faroe Islands, Fiji, Finland, France, French Polynesia, Germany, Greece, Greenland, Grenada, Guadeloupe, Hong Kong, Hungary, Iceland, Italy, Jamaica, Japan, Latvia, Liechtenstein, Lithuania, Macau, Mauritius, New Caledonia, New Zealand, Norway, Poland, Réunion, San Marino, Seychelles, South Korea, St Barthélemy, St Kitts and Nevis, St Lucia, St Pierre and Miquelon, Slovakia, Slovenia, St Vincent and the Grenadine, Switzerland, Taiwan, Trinidad and Tobago, Turkey, Vatican City, Vietnam
Those entering the UK from the common travel area - the Republic of Ireland, the Channel Islands, or the Isle of Man - are exempt, as are the 14 British Overseas Territories.
Health measures like quarantine are set by each UK nation separately.
Wales and Northern Ireland have introduced quarantine exemptions for the same countries as England. Scotland is also allowing exemptions, and has updated its own list of countries with which it is now allowing travel without quarantine.
Which other countries are not on the list?
You must isolate for 14 days if you arrive in the UK from Canada, the US, much of Central and South America, and some countries in Africa, the Middle East and Asia.
Travellers from Sweden, Portugal, Russia and anywhere else not on the list also have to quarantine.
Further restrictions may also be placed on UK travellers if its infection rate rises.
What about restrictions at my destination?
Travellers leaving the UK could still face restrictions - including quarantine - when they arrive in one of the exempted countries.
About half the countries and territories on the list have restrictions for arriving UK visitors. These include:
- UK visitors to France must quarantine for 14 days
- New Zealand has barred almost all foreign travellers
- Australia requires an exemption visa if you are not a resident or a citizen and everyone entering needs to quarantine for 14 days
- South Korea requires all arrivals to be tested and to isolate for 14 days
- Adult visitors to Iceland can either pay for a test or go into quarantine, with a second test required if you plan to stay 10 days or more
- Anyone who has been in the UK in the previous 14 days is not currently allowed to enter Japan
- 1 day ago
- 4 August