But last night one scientist demanded greater transparency over the number that shut down swathes of the UK.
Carl Heneghan, Professor of Evidence Based Medicine at Oxford University’s Nuffield Department of Primary Care, expressed scepticism over the 70 per cent figure.
He said: ‘I’ve been doing this job for 25 years and I can tell you can’t establish a quantifiable number in such a short time frame.’
He added ‘every expert is saying it’s too early to draw such an inference’.
Professor Heneghan said there was no doubt this time of the year, the ‘height of the viral season’, was a difficult time for the NHS. But he said failure to put out the basis of the figures was undermining public trust.
He added: ‘I would want to have very clear evidence rather than ‘we think it’s more transmissible’ so we can see if it is or not.
‘It has massive implications, it’s causing fear and panic, but we should not be in this situation when the Government is putting out data that is unquantifiable.’
He added: ‘They are fitting the data to the evidence. They see cases rising and they are looking for evidence to explain it.’
The new variant was found on September 20 in Kent.
By mid-November, 28 per cent of cases in London were attributable to it. And in the week starting December 9, it was responsible for 62 per cent.
Announcing the new Tier Four restrictions, Boris Johnson blamed the new Covid strain and said ‘it may be up to 70 per cent more transmissible than the old variant’.
He also said the new virus could boost the reproduction rate – known as R – by 0.4. When R is above 1 the virus is increasing. If it is below 1, it is decreasing.
Mr Johnson said the figure, which came from analysis by government advisory body The New and Emerging Respiratory Virus Threats Advisory Group (Nervtag), was ‘early data’ and ‘subject to review’.
But he added: ‘It’s the best we have at the moment.
‘We have to act on information as we have it because this is spreading very fast.’
Peter Horby, chairman of Nervtag and Professor of Emerging Infectious Diseases at the Centre for Tropical Medicine and Global Health at the University of Oxford, said the figure of 70 per cent was based on ‘converging data’.
He said: ‘This is including, but not limited to, the rate of change in the frequency of detection of the variant (the growth rate) and the correlation between R values and the frequency of detection of the new variant.’
Minutes from the Nervtag meeting from December 18 said they had ‘moderate confidence’ that the new variant, known as VUI-202012/01, ‘demonstrates a substantial increase in transmissibility compared to other variants’.
The variant demonstrated exponential growth when national lockdown measures were in place, the minutes added.