Theresa May's plan to approve a new wave of selective grammar schools is "socially divisive" and will lower standards for the majority of pupils, the chief inspector of schools has warned.
Ofsted chief Sir Michael Wilshaw used one of the Prime Minister's slogans while attacking her proposals, insisting new grammars would only work "for the few".
Mrs May has repeatedly insisted she wants to created a country that "works for everyone, not just the privileged few".
But Sir Michael, who will stand down in December, urged the PM to instead create specialist vocational schools led by employers and based on the models employed by the likes of Germany, Switzerland and Norway.
"If you're going to make a success of Brexit, this is number one," he told The Observer.
"It should be the number one government priority - not grammar schools.
"I came into teaching and I came into this job to raise standards for all children, not just for the few. And by their very nature grammar schools are for the few - otherwise why have them?
"It will actually lower standards for the great majority of children. That is my view. And it is socially divisive as well."
The Government has promised there will be no return to the "11 plus" entrance exam for grammar school pupils and insists Britain already has a "postcode lottery", with richer parents moving to areas with better comprehensives.
Mrs May has also stressed that new grammars will have to show they are "genuinely reaching out" to poorer pupils and that education is "not going back to the 1950s".
But Sir Michael said: "If you're taking away the best kids from the comprehensive system, you're creating, by another name, secondary moderns. You can call it what you like. People will know that the brightest children, the most academic children, are not going there."
He also said grammars would inevitably make it more difficult to attract the brightest teachers to non-selective schools.
Several Tory MPs including former education secretary Nicky Morgan and Commons Education Committee chair Neil Carmichael oppose Mrs May's plan for new selective schools.
But because it would only apply to England, the Government should have the majority required to get the plan through the Commons as the SNP would not take part in any vote, although the party has indicated it may be willing to block the plan if it has budgetary implications for Scotland.
Liberal Democrat leader Tim Farron said: "This deals a hammer blow to Theresa May's reckless and divisive plans to expand grammar schools.
"Selective schools don't do anything to improve social mobility - we know they admit far fewer pupils from disadvantaged backgrounds.
"It's about time the Government listened to expert advice and put this wrong-headed policy on the scrapheap."