Lockdown is unlikely to be eased significantly until daily Covid cases are in the hundreds, compared with more than 10,000 a day now, The Telegraph understands.
But the plan is unlikely to commit to a clear timetable for the coming months, instead promising a series of reviews which would see the reopening of shops, pubs and restaurants deferred until cases reach a low not seen since August.
Covid cases have fallen significantly in recent weeks and could reach less than 1,000 a day by early April if they continue to decline at the current rate. However, this is likely to be delayed by the impact of the return of schools.
A senior Whitehall source said: "For any significant relaxation of lockdown, household mixing and reopening pubs, case numbers have to be in the hundreds, not thousands.
"The numbers are coming down quite fast, but the plan is likely to be high level and set out the tests that have to be met for restrictions to be released. There is real reluctance about committing to specific dates without knowing what the case numbers are doing."
It came on the day it was announced that an additional 1.7 million people had been put on the Government's shielding list, suggesting they may be asked to restrict their movements while others return to work.
When Mr Johnson announced the third national lockdown on Jan 4, he said the plan for taking the country out of the restrictions depended on three factors – the success of the vaccination programme, the capacity of the NHS and the fall in deaths.
However, in recent weeks ministers have repeatedly highlighted the need for case numbers to fall significantly before restrictions can be eased, but without citing a specific threshold.
On Tuesday, Nadhim Zahawi, the vaccines minister, declined to say how low infections must be in order to allow the lockdown to be relaxed, telling Sky News: "The Prime Minister is right to say that where we are today in terms of number of people in hospital, in terms of case numbers per day, is still far too high, and we want to make sure we bring that right down. But I wouldn't want to speculate on this until we see more data."
Tory MPs on Tuesday night accused the Government of "moving the goalposts" in the promises made to the public.
Mr Johnson is expected to announce some kind of return to schools in England from March 8, but little else in terms of lockdown easing is expected because of the emphasis on case numbers. The Government is expected to announce a testing blitz next week which will see 400,000 rapid flow tests posted to homes and workplaces every day, it was reported on Tuesday night.
Nicola Sturgeon has announced that the youngest primary school pupils will return to classrooms in Scotland next Monday, but the vast majority of older children will remain at home for at least another month.
Scientists have said the return of schools could push up the 'R' reproduction rate of the virus by 0.4, which would mean it would take longer for cases to fall into the hundreds.
There were 10,625 Covid cases recorded on Tuesday, compared with more than 60,000 a day in the first week of January. However, cases have been above 1,000 a day since August after reaching a low of 370 in early July, around the time that pubs, bars and restaurants were reopened.
A Whitehall source said ministers remained hopeful that some outdoor mixing, such as playing tennis or golf, would be allowed in March, with shops allowed to open in April and pubs in May. However, the plan is likely to set out a series of data reviews, expected to be every three weeks, meaning the timetable could be altered depending on infection levels.
A major study by Public Health England examining the impact of vaccines on virus transmission is not expected to be published until March, after the roadmap.
On Monday, Mr Johnson met Rishi Sunak, the Chancellor, Matt Hancock, the Health Secretary, and Michael Gove, the Chancellor of the Duchy of Lancaster, to talk about a draft of the plan, with significant changes still under discussion.
The UK has now offered vaccines to more than 16 million people, including everyone over the age of 70. On Tuesday, Office for National Statistics data suggested the programme is beginning to show an impact, with antibodies found in more than four in 10 people aged 80 and over.
On Tuesday night, Sir Graham Brady, the chairman of the influential 1922 Committee of Tory backbench MPs, told The Telegraph: "The case for the current lockdown was made on the grounds that NHS ICU [intensive care unit] capacity was about to be overwhelmed.
"Now the picture is profoundly different. All of the most vulnerable groups have been vaccinated. Positive test numbers, hospitalisations, deaths are all falling rapidly.
"The presumption should be that people are given back control over their own lives and we move from a world of arbitrary regulation to one where we are able to take responsibility for ourselves and each other. We cannot allow the goalposts to be moved every time we are about to reach freedom."
On Tuesday, Chris Hopson, the head of NHS Providers, wrote to Mr Johnson to tell him that "data rather than dates" should be the way out of lockdown.
Mr Hopson highlighted calls from scientists to reduce daily case numbers to less than 1,000 before easing restrictions, saying hospital leaders believe the NHS will remain at "full stretch" for at least six weeks.