Rishi Sunak was facing a major Conservative rebellion minutes after the applause died down on his first conference speech as Prime Minister.
Tory MPs, led by Liz Truss, have reacted strongly against his plans to ban smoking by raising the age limit by a year every 12 months.
Although, Mr Sunak said the annual vote would be “a matter of conscience” and a free vote for MPs, the idea has been lampooned by some of his backbenchers and condemned for being anti-freedom.
In particular Ms Truss, who was removed in a coup by Sunak’s supporters after 49 days last year, has come out against the party.
A source close to her made it clear she opposes the decision not long after the Institute for Economic Affairs (IEA) had attacked it.
A source close to Ms Truss said: “She will vote against the proposal to raise the legal age for purchasing tobacco year by year.
“You will recall that in her speech on the fringe on Monday she talked about the need for Conservatives to ‘stop banning things'”.
Meanwhile, other influential MPs have publicly attacked the plans.
Chairman of the influential Common Sense Group Sir John Hayes said: “If the Prime Minister had wanted to raise the smoking age to 21 then most people would have supported him.
“But this is a ludicrous idea and will end up with 40-year-olds being allowed to smoke but 39-year-olds not at some point.
“People will forever be having to confirm their age. I can’t imagine why the Prime Minister has been persuaded by this madness.”
Shipley Conservative MP Philip Davies, who is a GB News presenter, called the plan an attack on personal freedom.
He said: “I will be voting against the anti-freedom, anti-personal responsibility smoking age policy – silly idea and completely unenforceable.
“In 40 years’ time, are we really going to be asking 60 year olds for age ID?”
Simon Clark, director of the smokers’ rights group Forest, said: “These are desperate measures by a desperate prime minister.
“Raising the age of sale of tobacco is creeping prohibition, but it won’t stop young people smoking because prohibition doesn’t work. Anyone who wants to smoke will buy tobacco abroad or from illicit sources.
“This is the opposite of levelling up, it’s dumbing down. Future generations of adults who are considered old enough to vote, pay taxes, drive a car and drink alcohol are going to be treated like children and denied the right to buy a product that can be purchased legally by people a year older than them.”
Mr Sunak though warned that there was no level of smoking which “is not harmful” and said that the health problems caused by smoking made the measure vitel.