Boris Johnson is set for a “battle royal” with Conservative MPs over his expected cautious approach to easing England’s lockdown after the 15m people considered most vulnerable to coronavirus have been vaccinated.

The UK prime minister does not intend to rush into easing the nationwide lockdown restrictions which are set for review on February 15, according to allies. The government estimates that 88 per cent of likely deaths associated with Covid-19 will be cut as a result of the initial wave of inoculations.

But the Covid Recovery Group of 50-plus Tory MPs who are sceptical of lockdowns has urged Mr Johnson to set out a road map for exiting the restrictions by March 8, three weeks after the most vulnerable are due to be vaccinated and some immunity has developed.

The current restrictions automatically expire in law on March 31 and the legislation will have to be renewed if the tiering system of restrictions returns — a likely flashpoint with Tory MPs.

One influential member of the CRG warned that the prime minister might have to rely on opposition votes to pass the measures. “I don’t see how they have the [Conservative] votes to get this through again.”

The Labour party has backed all the lockdown measures to date.

Individuals with understanding of Mr Johnson’s thinking said that the prime minister had heeded the lessons of overpromising and under delivering on Covid-19 measures and did not want to undermine the plaudits he had received for the rapid vaccine rollout.

“Boris wants this to be the last lockdown, even if it has to go on longer. There has to be a sense of finality to these measures so he appears to be on side with the scientists,” the individual said. “He is being cautious”.

The decision on how to exit the lockdown will require a decision on what level of infection Mr Johnson, who was admitted to intensive care last April after falling ill with Covid-19, is willing to accept among the rest of the adult population. A Whitehall official said: “It is going to be a risk-based judgment on how high you are willing to let infections run. It isn’t a decision for scientists, it’s a political call”.

One senior Tory MP predicted a “battle royal” between Conservative MPs and the government. “There is a big question about what happens when we hit the target of vaccinating 88 per cent of people who could have died and whether you are then prepared to take some risks to get the economy going again.”

The MP added: “[Health secretary] Matt Hancock has indicated to backbenchers he might be prepared to take some risks once vaccinations have reached a certain point, but I think Boris might be more cautious. His argument is that we have got ahead of the game on the vaccine — why risk it now?”

One way to appease Tories with the March 31 deadline may be to tweak the legislation to ensure more frequent parliamentary scrutiny. “The regulations could be reviewed in a different way as a compromise, maybe renewed for a shorter period. There's no appetite for any kind of rebellion against the PM,” one senior party figure said.

Patrick Vallance, he government’s chief scientific adviser, warned on Wednesday that “waiting and watching simply doesn't work” in tackling Covid-19 and cautioned against easing the current lockdown too soon.

“The lesson is go earlier than you think you want to, go harder than you think you want to, and go a bit broader than you think you want to in terms of applying the restrictions,” he told Sky News. Sir Patrick added that the exit strategy would more likely take the form of a “slow release” instead of a “big bang”.

There is also widespread concern in Whitehall that rushing to exit the lockdown could risk overwhelming the NHS. “There is a danger that the new variants spread so rapidly it could still overwhelm the NHS. That means more of the adult population will need to be vaccinated before things can properly open up,” one official said.

Discussions are under way across departments about a gradual exit strategy, which may see most of England return to the highest tier 4 restrictions — including schools reopening — in March. Different regions of England would then proceed through to lower tiers as infections drop.

There is hope among ministers that some areas of England could return to the tier 2 restrictions by the Easter, the first weekend in April, to allow pubs and restaurants to reopen and families to socialise outdoors.

But one senior Number 10 official said any discussions about dates were “wrong”, adding: “No decisions made and we aren’t at that point yet, it’s too early”.