In the end it may come down to what happened during three crucial days in April.
As cases of the highly transmissible new Indian variant of Covid begin to rise in parts of Britain, questions are being raised as to how it was allowed into the country in the first place.
Alarming reports of the spread of a new highly infectious variant of Covid on the Indian subcontinent first emerged early last month.
The Government acted by adding Pakistan and Bangladesh – India’s direct neighbours – to its "red list" on April 2, barring foreign travellers and forcing 10-day hotel quarantines on returning UK citizens.
The decision led to concerns among epidemiologists, who questioned why India was not included.
Health officials had started to detect an increase in the arrival of Covid cases from India. Public Health England (PHE) data now shows that of the 3,345 people arriving from India between March 25 and April 7, 4.8 per cent tested positive, compared to 0.1 per cent of people in England.
PHE also detected the arrival of three Indian variants around the UK. The most worrying of these, B1.617.2, which is spreading most quickly and has claimed at least four lives here so far, was initially detected in tests carried out on travellers arriving from India during the week ending March 29. According to PHE, at least 122 passengers arriving from Delhi and Mumbai between late March and April 26 were carrying this "variant of concern".
With India not on the “red list”, all but a handful of these travellers would have been allowed to leave the airport and travel home, as well as being asked to self isolate.
Meanwhile, Boris Johnson, the Prime Minister, was determined to press ahead with a planned visit to India on April 25.
The plan was that he would be able to announce that early discussions were now under way over a new trade deal. But as more and more data from India began to ring alarm bells, he came under pressure to call off the trip. Downing Street eventually pulled the plug on April 19, on the same day Matt Hancock, the Health Secretary, told the House of Commons that India would also be added to the red list – but only from 4am on April 23.
This was despite Downing Street having briefed journalists when the scheme was first unveiled that countries could be added "at a few hours' notice".
The result of the three-day delay was inevitable. Demand for flights between India and the UK rocketed amid a “desperate frenzy'” as families tried to beat the deadline and avoid having to quarantine in a hotel. Thousands of extra passengers travelled into Britain from the subcontinent.
On April 19, Labour’s shadow home secretary Nick Thomas-Symonds criticised the delay, telling LBC: “It is not good enough to try and shut the door after the horse has bolted, by adding countries onto a ‘red list’ when it is too late.”
On April 20, Professor Sir Mark Walport, former chief scientific adviser to the Government, admitted the ban on travel from India had been tardy, telling BBC Breakfast: “These decisions are almost inevitably taken a bit too late, in truth, but what's absolutely clear is that this variant is more transmissible in India.”
Mr Johnson on Friday defended the delay in adding India to the “red list”, saying cases at the time had been higher in Pakistan.
Asked why India was not added to the “red list” on April 2, along with Bangladesh and Pakistan, Edward Argar, the health minister, also told BBC Radio 4's Today programme on Saturday that India had a good genome sequence programme and therefore a new variant was not considered such a threat at the time.
But the impact of the delay in implementing the travel ban appears to have been reflected in the numbers of cases.
Between April 4 and May 2, the B 1.617.2 variant rose from 4.9 per cent of all cases detected among travellers, to 40.9 per cent. The single biggest increase came in the week which included the three and a half days between the afternoon of April 19 and the early morning of April 23.
On Wednesday, May 5, a Sage meeting concluded there had been a “significant recent increase in prevalence of the B.1.617.2 variant, including some community transmission”. They warned “early indications... are that this variant may be more transmissible than the B.1.1.7 [Kent] variant.”
Realisation of the growing threat posed by the Indian variant had a dramatic impact on the mood at Number 10. On May 10, Mr Johnson was still in a characteristically confident mood. Announcing the biggest easing of lockdown so far, with indoor dining and drinking allowed from May 17, he declared Britain was on the “road back to normality”. There was even talk inside Downing Street of doing away with face masks and ending social distancing for good.
But that same day a meeting of the Variant Technical Group under the chairmanship of PHE’s national Covid-19 incident director was shown evidence of the alarming spread of B.1.617.2. Modelling showed the NHS could yet again be overwhelmed.
The meeting concluded: “If B.1.617.2 does have such a large transmission advantage, it is a realistic possibility that progressing with all roadmap steps would lead to a substantial resurgence of hospitalisations.”
These concerns were relayed to Downing Street and had a marked impact on the Prime Minister’s mood. On May 12, he told the Commons the Indian variant was now of “increasing concern” and could pose “a potentially lethal danger”.
Over the next 48 hours two main courses of action were decided by the Government. The first was to “flex” the vaccine rollout so that around 10 million over-50s or in vulnerable categories will now get their second vaccine after eight weeks, rather than 12.
The second was to bring surge testing on the ground in Bolton.
A Sage meeting on May 13 then suggested there is a "realistic possibility" that the Indian variant of Covid-19 is 50 per cent more transmissible than the one that emerged in Kent. The group of scientists said that if higher levels of transmissibility are confirmed, moving to step three of the roadmap on Monday could "lead to a substantial resurgence of hospitalisations (similar to, or larger than, previous peaks)".
SAGE has said there is no clear evidence that this variant causes more serious illness but government advisors have warned vaccines are “almost certainly less effective” at reducing transmission of Indian variant.
If B.1.617.2 establishes itself as the dominant strain in the UK – sending numbers of cases surging once again – it could threaten all the suffering and sacrifices of the third lockdown and raise the prospect of renewed restrictions.
And that would beg the question of why Mr Johnson left it so late to impose restrictions on travel from India, and why travellers were allowed those extra three and a half days to come to the UK.