Rishi Sunak’s public health policy banning the next generation from being able to buy cigarettes is to be introduced in parliament this week, with officials braced for a backlash from Conservative rebels. While the policy commands considerable support in Conservative ranks, the scale of an expected rebellion by libertarian Tories – whose ranks includeLiz Truss – has yet to become clear. However, sources involved in lobbying to defeat the bill claim that as many as 80 to 100 MPs are unhappy, setting up a scenario in which Sunak would be reliant on Labour for what may yet emerge as one of his few legacy policies. Tory MPs who were planning to oppose the bill told the Guardian that the scale of opposition would be dependent on what is in it and how it is amended. A first reading is expected to take place in the House of Commons on Wednesday, in what is usually a formality and takes place without a debate – although it may yield some clues as to the scale of unhappiness among Tories. Under the plan, first reported in the Guardian, anyone born on or after 1 January 2009 – in effect anyone who is 14 or younger now – will not legally be able to buy cigarettes in England during their lives as the smoking age is raised by one year every year, subject to MPs’ approval. Since Sunak announced the policy at the Tory party annual conference last year, the Conservative government of New Zealand has said that it is to revoke the country’s own policy on banning smoking, which served as the prime minister’s blueprint. John Hayes, a former minister and influential Tory backbencher on the right of the party, questioned on Monday whether the legislation would ultimately be workable, criticising a scenario in which a person aged 28 would be deemed capable of buying tobacco, while someone at 27 would not. He told the Guardian: “I’m in favour of reaching age consent for smoking and many other things. I think any legislation has to be based on whether it can be implemented, whether it will be done. I don’t think this is practically possible.” However, Sunak is likely to be helped by MPs who have had a change of heart about health interventions. Alun Cairns, a Tory MP and former secretary of state for Wales, said that he had opposed such a ban in the past, believing that “the market” would ultimately deliver a better outcome, but added that he had come around to the public health arguments, as many others had too. Before a meeting of centrist One Nation Tories on Monday evening, Flick Drummond, the MP for Meon Valley in Hampshire, said: “Although I understand the views of those who feel the state is getting far too involved in people’s lives, I’m very much in favour of a smoking ban because treating those who have smoked is a huge and expensive public health challenge as well as a human tragedy because it kills people so early. “Many Conservatives, who instinctively would usually be reticent about such an intervention and who don’t like banning things, do share my view because smoking and passive smoking is so dangerous.” She believed there was widespread support for the ban among many Conservative MPs, reflecting the public mood. “Luckily lighting up holds very little attraction these days for the public and I believe there is widespread support for a ban. For all these reasons, I imagine that view would be reflected among many Conservative MPs,” she added. A survey last month by the public health charity Action on Smoking and Health (ASH) found that 71% of adults supported the goal of making Britain a country where no one smokes, while 12% are opposed.