Boris Johnson has blasted Rishi Sunak's plan to ban smoking for future generations, branding it "barmy" and unworkable.
The ex prime minister said Mr Sunak's proposal would "criminalise yet another variety of ordinary behaviour" with "no thought to the consequences for those who have to make it work".
The PM announced during his conference speech in Manchester this week that the government would legislate to gradually raise the smoking age ever year so that a child who is 14 or under today would never legally be allowed to buy cigarettes.
The limit would start rising from 2027 with the cut-off on 1 January 2009. A similar policy was approved in New Zealand last year and is set to take effect.
Writing in his column for the Daily Mail newspaper, Mr Johnson described the plan as "smoking apartheid" and said the habit would die out eventually on its own accord.
"Child A will be free to smoke like a chimney to the end of his days. Child B — born only a day later! — will be a criminal if he does. How the hell is that supposed to work?" he said.
"Will shops have to demand ID cards from middle-aged customers, to show they were indeed born before January 1, 2009? And how will we check, in the decades to come, that A is not buying cigarettes for B?"
"As a habit, smoking tobacco is less and less popular among young people, and in a few years’ time I expect the whole idea — of sucking smoke and tar into your lungs — will die of disapproval.
"But are we really going to ban something that remains legal in every other country in the world?
He said the ban would come in just as other countries such as the US were "actually liberalising their laws on other smokable substances", referring to cannabis – which is increasingly legally available in many countries.
Other Conservatives, such as Liz Truss have already criticised the plan – making Mr Johnson the second former prime minister to set himself against it.
The plan has however been welcomed by health campaigners who say it will cut cancer deaths and save the NHS money. Labour has also said it would back the policy. Mr Sunak has said he will give his MPs a free vote on the issue.
This week Mr Johnson had also, along with David Cameron, criticised Mr Sunak's decision to scrap the northern phase of the High Speed 2 railway project.
