Ministers have been accused of paving the way for more selective schools by the back door, without the need for a risky vote in Parliament.
Campaigners against grammars have seized on a clause in Government proposals to allow multi-academy trusts (MATs) to create a single “centre of excellence” within their chain of schools.
They fear the trusts will move their brightest pupils into that centre – which will, effectively, become a grammar – while less academic children will be shunted to other sites.
Becky Allen, director of the think-tank Education Datalab, said: “I think [the Government] could circumvent the need for legislation to go down this route of selection within MATs.”
The back door route to selection has been uncovered by the online magazine School Week, which has highlighted how the Department for Education (DfE) has shifted its ground.
In March, Schools Week was told that schools could not select by ability and that any trust found to be moving its pupils around on this basis would be investigated for a breach of the school admissions code.
But it says the DfE appears now to have abandoned that stance, arguing instead that pupils of both low and high ability could be moved between schools in a multi-academy trust.
The green paper introduced by Education Secretary Justine Greening stated moving the brightest pupils into a “centre of excellence” is “permissible”.
Schools Week has been told that, providing pupils remain on the roll of the school they were admitted to - and receive some of their education there - schools could teach pupils at another school or site.
It quoted the DfE saying a school move should not be done without parental consent, but failing to state what action would be taken if parental consent was not granted.
A spokesman said the proposals in the green paper consultation would require changes to legislation, but would not confirm if this applied to the “centres of excellence”.
Schools Week believes parents of pupils selected to enter a “centre of excellence” would consent to their child moving, arguing this would effectively turn the trust’s remaining schools into secondary moderns.
Multi-academy trusts are believed to be uneasy about selection but, last week, Sir Dan Moynihan, chief executive of the Harris Federation, said he might be convinced to open a selective school.
A DfE spokeswoman said scrapping the ban on new grammar schools would “provide stretching education for the most academically able, regardless of their background and help to eliminate the attainment gap between disadvantaged pupils and their peers”.
She added that “there will be strict conditions that grammar schools must make sure they improve the education of pupils in every other part of the system”.
Theresa May is faced with possible defeat on her first flagship policy, after more than a dozen Tory backbenchers criticised grammars, some warning of the “stigma” for pupils denied places.
