Opposition to new grammar schools is growing among Conservative MPs, threatening Theresa May with possible defeat over her first flagship policy.
Tory backbenchers lined up to criticise the shake-up – some warning of the “stigma” for pupils denied places – while others expressed doubts about a return to selection.
More than a dozen Conservative MPs have now spoken out, a growing headache for the Prime Minister who has a working Commons majority of just 17.
There was also criticism of another aspect of the proposals, the move to scrap the 50 per cent cap on pupils of a single religion when allocating places in new faith schools.
Tory veteran Ken Clarke warned of “very considerable dangers”, adding: “We need to live in a society where we reduce barriers and improve contacts and integration between people of all faiths.”
Meanwhile, outside the Commons, the “terribly retrograde step” was attacked by Professor Ted Cantle, who wrote a report on tackling segregation after 2001 race riots in Northern towns.
“We really can’t have children from different backgrounds who are growing up in isolation from each other, with no understanding of each other,” the academic said.
The escalating opposition to grammars was revealed when Education Secretary Justine Greening gave a statement to MPs, three days after the prime minister announced the policy.
A £50m-a-year pot will be set aside for expanding selection, with five councils, some of which are fully comprehensive, already considering the creation of new grammar school places.
But one Tory backbencher, Alec Shelbrooke, said: “I’m quite worried about what I’ve heard so far. How do you not create a stigma for those who don’t go to the selective entry school?”
Another, Ben Howlett, warned: “There is no evidence to suggest, thus far, that social mobility will be improved by opening up new grammar schools.”
And Keith Simpson, who attended a grammar school, attacked their expansion, saying: “I often wonder, if I had failed the 11-plus, where I would be. I know I would not be here today.”
Contrary to earlier hints, former Education Secretary Michael Gove did not give his backing to the grammar school plan, although he praised Ms Greening’s “clear moral purpose”.
The world's toughest school run
The world's toughest school run
Children carry their schoolbags climb on a cliff on their way home in Zhaojue county in southwest China's Sichuan province
Children carry their schoolbags accompanied by adults climb on a cliff bu using ladder as they on their way home in Zhaojue county in southwest China's Sichuan province
A child carry her schoolbag looks as she takes a rest on a cliff as she and other children on their way back to home in Zhaojue county in southwest China's Sichuan province
A village in China's mountainous west where schoolchildren must climb an 800-meter (2,625-foot)-high bamboo ladder secured to a sheer cliff face may get a set of steel stairs to improve safety
Schoolchildren carry their schoolbags climb on a cliff on their way home in Zhaojue county in southwest China's Sichuan province
Pressure was also applied by the respected Institute for Fiscal Studies (IFS), which issued a study concluding: “There is robust evidence that attending a grammar school is good for the attainment and later earnings of those who get in.
“But there is equally good evidence that those in selective areas who don’t pass the eleven plus do worse than they would have done in a comprehensive system.”
At least five times, Ms Greening referred to starting “a debate” on more grammars – again hinting at her lack of enthusiasm for a policy driven by No10.
However, she insisted more selection could improve attainment, adding: “For most children the chance to attend a selective school simply does not exist.
“We will therefore look at how we can relax the rules on expanding selective schools, allow new ones to open and non-selective schools to become selective where there is a demand.”
Labour told her to “stop your silly class war” – pointing out the phrase had been used by David Cameron when speaking out against expanding grammars.
Angela Rayner, the shadow Education Secretary, said: “Where once, under Labour, we had 'education, education, education', this Government's mantra is segregation, segregation, segregation.”