The UK's "red list" of countries - from which entry to the UK is banned - has been expanded to include Bangladesh, Pakistan, Kenya and the Philippines.
The changes, which came into force on 9 April, follow concerns about the spread of new variants of coronavirus in these countries.
There are fears that vaccines may not work quite as well against these strains.
Which countries are on the red list?
The changes mean there are nearly 40 countries on the government's red list of countries from which travel is banned:
- Middle East: Oman, Qatar and United Arab Emirates (UAE)
- Africa: Angola, Botswana, Burundi, Cape Verde, Democratic Republic of the Congo, Eswatini, Ethopia, Kenya, Lesotho, Malawi, Mozambique, Namibia, Rwanda, Seychelles, Somalia, South Africa, Tanzania, Zambia, Zimbabwe
- Asia: Bangladesh, Pakistan, Philippines
- South America: Argentina, Bolivia, Brazil, Chile, Colombia, Ecuador, French Guiana, Guyana, Panama, Paraguay, Peru, Suriname, Uruguay, Venezuela
Countries can be added to the list with just a few hours' notice.
What is the traffic light system - and is it different from the red list?
For England, when holidaying is allowed, destination countries will be put in one of three colour-coded categories - with different rules for returning travellers.
Red - Countries on the red list will be in this category. British nationals or residents returning to the UK will have to pay for 10-day hotel quarantine. Non-British nationals/residents who have passed through red countries will be refused UK entry.
Amber - Details yet to be given, but it could require 10-day return quarantine at home, with possible early release after a negative test.
Green - No isolation needed, but pre-departure and post-arrival tests required
What are the hotel quarantine rules?
If someone has been in or through any red-list countries in the previous 10 days, they will be refused entry to the UK.
An exception is made for British or Irish passport holders - or people with UK residence rights - but they must first pay to quarantine in a government-approved hotel for 10 days.
In England, this costs £1,750 per passenger travelling alone, to cover transport, tests, food and accommodation.
Every additional adult, or child over 12, must pay £650, while children aged five to 12 pay £325.
They must also have proof of a negative coronavirus test to enter the UK.
Rule-breakers face strict penalties - including prison sentences of up to 10 years.
Could European countries end up on the red list?
Health minister Lord Bethell has said it's possible the UK's nearest neighbours could be added "with huge regret".
Portugal (including Madeira and the Azores) was on the list, but was removed on 19 March.
Under lockdown rules, holiday travel is not currently allowed - either in the UK or abroad.
You can only travel abroad for essential reasons - the same as the "reasonable excuses" for domestic travel, including:
- Work that cannot be done from home
- Medical appointments
- Educational reasons
What are the testing rules when I get back to the UK?
All travellers to the UK must complete a passenger locator form in advance, including their departure country and UK address.
They also have to show proof of a negative Covid-19 test taken within 72 hours before travelling to be allowed entry.
Travellers must then self-isolate for 10 days on arrival..
There are specific rules for people arriving in each UK nation:
Returning travellers must take a coronavirus test on days two and eight of quarantine, at a cost of £210. If they test positive, they must self-isolate for a further 10 days.
There is a £1,000 penalty for not taking the test, followed by a £2,000 fine for failing to take the second one, with quarantine automatically extended to 14 days.
Can I pay for a test to shorten quarantine?
Under the "test to release" scheme, travellers from some countries can take a test on day five of isolation.
People who test negative can stop isolating. Those who test positive must quarantine for 10 more days after the test.
Anyone using the scheme still has to take a further test on the eighth day.
Tests cost between £65 and £120.