Yvette Cooper, the Labour MP who chairs parliament's Home Affairs Committee, has criticised the delays in putting India on the government's travel-ban "red list".
"Why did PM not put India on the red list 2 weeks earlier when Pakistan and Bangladesh were added to red list? And why did they then delay a further 4 days to implement?" she tweeted.
One of the variants of coronavirus first identified in India has spread to the UK. Just under half of these cases involve international travel and the strain has now been designated a "variant of concern".
India was added to the red list on 23 April, but neighbouring Pakistan and Bangladesh have both been on it since 9 April.
What is the red list?
The red list is the government's list of 43 countries from which there are strict restrictions on travel to England.
The restrictions are designed to protect the UK from new variants of Covid, against which existing vaccines may be less effective.
Travel to England is banned for anyone who has been in one of the countries in the past 10 days, except for UK citizens and residents, who have to isolate on arrival at government-approved hotels for 10 days.
What are the criteria for going on the red list?
The decision is based on Joint Biosecurity Centre risk assessments, which include:
- how good a country's testing structures are, including checking for variants of concern
- how many cases those systems have identified
- whether people in that country have been catching new variants at home or the cases have come from overseas
- evidence of whether that country has exported cases of new variants to other countries, including to the UK
- how good the country's travel links with the UK are
The first point on the list is important, because the genome sequencing needed to identify new variants is very sophisticated and relatively rare.
But just because a country has found new variants, or has many cases of coronavirus, it will not necessarily be on the red list.
On 11 May, the World Health Organization identified:
- 102 countries where the variant identified in South Africa had been found, of which 26 are on the red list
- 60 countries with the variant identified in Brazil, of which 20 are on the red list
- the variant of concern identified in India has been reported in 31 countries.
Why were Pakistan and Bangladesh put on the red list before India?
Bangladesh had the South Africa but not the Brazil variant and Pakistan had neither when they were added to the red list on 9 April.
India had both, as well as a new variant, but was not added for another two weeks.
On 9 April:
- Pakistan had a seven-day average of 21 cases per million people
- Bangladesh had twice as many
- India had four times as many
In late March, India's health authority said 771 variants of concern had been detected in a sample of almost 11,000 positive cases - a fraction of the millions of cases recorded in the country.
India has a greater sequencing ability than Pakistan or Bangladesh, although it is far behind the UK, which does about half of the world's sequencing.
We asked the government why India wasn't added before. Its response did not directly answer the question but said the red list was kept "under constant review".
"Nobody knows the full criteria - but there may be a political element because the UK wants a trade deal with India," Dr Simon Clarke, associate professor in cellular microbiology, at the University of Reading, said.
Boris Johnson cancelled a planned trade trip to India on 19 April.
"It's not always a data-driven decision," he added, giving the example of Somalia, which is on the red list but has one of the lowest official rates of infection and deaths in the world.
How many cases of the new India variant have been found?
Announcing the decision on India on 19 April, Health Secretary Matt Hancock said 103 cases of the variant had been found in the UK.
On 13 May, the government said the number of cases had risen from 520 to 1,313 in the past week.
One of the variants first identified in India was designated as a variant of concern on 7 May.
The WHO said it appeared to have a higher rate of transmission and that there was preliminary evidence suggesting some vaccines may be less effective against it.
Scottish First Minister Nicola Sturgeon cited fears of the India variant as one of the reasons why Glasgow and Moray will not have restrictions eased as planned.
How much is linked to international travel?
The Civil Aviation Authority said that in February 2021, 50,000 passengers travelled between India and the UK, which is an average of just under 900 a day in each direction.
We asked the government how many travelled from India to the UK between the announcement of the travel ban on 19 April and it coming into force on 23 April, but have not had an answer.
Just under half of people with the India variant of concern in England had been travelling, according to a briefing from Public Health England.
It said that about one third of the cases were in London and a quarter were in the North West of England. Almost 60% of positive Covid19 tests are now sent for genome sequencing to identify new variants, which means the government has a good idea of where the cases are.
Asked about the delays in adding India to the red list, the UK's former chief scientific adviser Prof Mark Walport told the BBC: "These decisions are almost inevitably taken a bit too late in truth."