The UK parliament will on Tuesday kick off its first debate on Prime Minister Rishi Sunak's planned legislation to prevent young people from ever smoking, despite opposition from many in his own Conservative Party.

The law would ban the selling of tobacco products to anyone born after January 1, 2009 –- effectively raising the smoking age by a year each year until it applies to the whole population.

"This has the potential to phase out smoking in young people almost completely as early as 2040," the government said when it unveiled the plan, calling the move "historic".

While the law looks set to pass thanks to support from opposition parties, Sunak faces the prospect of a rebellion from backbench Tory MPs.

The beleaguered leader has little political capital to expend within his fractured party as he struggles to revive its fortunes following months of dire polling.

Conservative MP Simon Clarke told BBC radio that he was "both sceptical and downright opposed" to the plans.

"I think that an outright ban risks being counterproductive, I think it actually risks making smoking cooler, it certainly risks creating a black market, and it also risks creating a unmanageable challenge for the authorities," he said.

Former prime minister Boris Johnson also said at an event in Canada last week it was "mad" that the party of Winston Churchill was "banning cigars".

However, opinion polls show that around two-thirds of people in the UK back a phased smoking ban.