Plans to test international travellers before departure to England have been delayed on the eve of the policy coming into action.
Passengers wishing to make a journey were told they had to provide proof of a negative coronavirus test from 4am on Friday 15 January before boarding.
But transport secretary Grant Shapps applied the brakes on the evening of Wednesday 13 January - here's why.
What is the test for travel policy?
The much talked about 'test before travel' scheme has been brought in to help reduce the international spread of Covid-19.
It requires passengers to take a government approved Covid test three days before departure and provide proof of the negative result before boarding to England.
Without a negative test result certificate, travellers might not be able to get on their flight, boat, or train as they may transmit the virus to other passengers on the journey.
Arrivals without proof of a negative test result could be fined £500.
Passengers still have to follow self-isolating rules when they arrive in England, even after providing a negative test to enter the country.
Why has it been delayed?
The policy was delayed by the transport secretary to allow travellers more time to prepare for their journey, amid confusion over which tests were approved by the government.
Grant Shapps tweeted: “To give international arrivals time to prepare, passengers will be required to provide proof of a negative Covid-19 test before departure to England from Monday 18 January at 4am.”
The delay meant some people scheduled to travel on Friday or Saturday who had already organised or taken a test now no longer need to provide proof of a negative test result.
In response, Craig (@Outnumbered5_1) asked how he could get a refund, adding: "Great, so I spend $200 and a good part of yesterday scrambling to get a test in time for my daughter who lands in the UK 10am Friday, which she now doesn’t need."
It's worth checking with your test provider for details on whether you're entitled for a refund.
When is it expected to start?
The policy will now take effect from 4am on Monday 18 January, with passengers arriving in England required to have taken a Covid test within the last 72 hours.
Labour MP Yvette Cooper, chairwoman of the Commons Home Affairs Committee, said it was "truly shocking".
She tweeted: "Questioned PM repeatedly today on why border testing/quarantine is weaker than other countries. Repeatedly he said Govt is bringing in new testing (months later than elsewhere but due Fri). But now it’s not. More delays. As they haven’t published guidance in time."
What type of test do I need to take?
The government's guidance now states that travellers will need to find a test provider, which meets the criteria for pre-departure testing.
PCR tests, nasal and throat swab tests, which take between 12 and 24 hours to return results, are listed along with LAMP tests, which can return results in two or three hours, and lateral flow tests, which can return results in less than 30 minutes.
Guidance states: "It is your responsibility to ensure the test meets the minimum standards for sensitivity, specificity and viral load details so you must check with your test provider that it meets those standards. You may not be able to travel if the test does not meet these standards."
Are there any exemptions?
Travellers who begin their journey in Ireland, Northern Ireland, Scotland, Wales, Isle of Man, Jersey or Guernsey, Ascension, Falkland Islands or St Helena will not need to take a test for a flight to England.
And, for a limited time, passengers who start their journey from Antigua and Barbuda, St Lucia or Barbados won't have to take a test before 4am on Thursday 21 January. Travellers will need to take a test after this time.
Children under the age of 11 and people with certain medical conditions or who are seeking urgent medical treatment do not need to take a test before travelling.