The PM gathered his Cabinet this morning as he prepares for the start of the draconian month-long restrictions in England.
But Mr Johnson is up against a growing backlash with many MPs questioning the scientific basis for the squeeze.
Critics have condemned the use of a chart suggesting daily deaths could rise to 4,000 by December, saying it is out of date and has since been withdrawn by the modellers themselves.
The measures – which mean non-essential retail, bars and restaurants will be shut from Thursday until December 2 and households will be banned from mixing indoors – are set to be approved by the Commons as Labour is supporting them.
But it will be hugely damaging for Mr Johnson if he has to rely on Keir Starmer’s votes to get the lockdown through.
The PM gathered his Cabinet this morning as he prepares for the start of the draconian month-long restrictions in England
The weekly Cabinet meeting was held in the Foreign Office as there is more room to socially distance than in Downing Street
There were signs this morning that the scale of the mutiny could be smaller than initially feared by ministers, with some rebels suggesting only 15-20 could end up voting against.
However, many are waiting for the publication of the legal regulations on the lockdown, and the full scientific evidence supporting the move.
The premier desperately tried to sooth anger on his backbenches yesterday by giving a firm commitment that the curbs will expire on December 2.
‘Whatever happens these restrictions end on December 2,’ he told the Commons.
‘I think there is the prospect of a much brighter future ahead if we can make a success of these national measures and open up again in December, to give people the chance of some shopping and economic activity in the weeks leading up to Christmas and beyond.’
The comments appeared to overrule Michael Gove, who sparked fury on Sunday by suggesting the lockdown could be extended.
Amid fears about the devastating impact on UK plc, the influential Treasury Select Committee has called for the government release an economic assessment before MPs decide.
The committee’s Conservative chairman, Mel Stride, said: ‘As part of our inquiry into the economic impact of coronavirus, the Treasury Committee has examined the wider modelling of the effects of the pandemic.
This slide presented on live TV on Saturday shows a projection of deaths hitting 4,000 per day by the end of December (blue line) but experts say they are ‘concerned’ about the decision to include this because it is based on old data that has since been updated
The 4,000 deaths per day scenario was based on the assumption that there would be 1,000 per day by the start of November. Real numbers of people dying are significantly lower, with an average 182 per day in England and 162 confirmed yesterday for the whole UK
‘To aid this inquiry, and also to assist MPs ahead of the vote on Wednesday on new lockdown measures, it would be helpful if the Treasury published the work that it has carried out in respect of the various interventions considered by the Government.’
In his letter to the Chancellor, Mr Stride referred to official minutes which disclosed that work has been carried out to examine the potential economic impact.
The September 21 meeting of the Sage scientific advisory panel referred to work ‘to analyse the economic impacts and associated harms of all interventions’.
Mr Stride told Mr Sunak: ‘I would be most grateful if the Treasury could provide the Treasury Committee with its analysis of the economic impacts and the associated harms of the interventions, referred to in the Sage minutes, including analysis of the specific lockdown that the Government intends to introduce on November 5.’
Cabinet minister Robert Jenrick suggested that an impact assessment has not actually been carried out.
The Communities Secretary told TalkRadio the Government ‘is taking advice’ about the economic cost.
But asked repeatedly whether there had been an economic assessment, he said: ‘There is not a specific document.’