Grammar schools claim they are being forced to axe courses, make teachers redundant and could face closure as a result of resources being diverted to low-achieving pupils.

Headteachers claim that selective schools - as well as comprehensives in more affluent areas - are the big losers in a funding regime where the focus has shifted towards children from deprived families.

The news comes as the issue of grammars is set to dominate the thoughts of the next education secretary under the new Conservative government. The decision about whether to allow Weald of Kent Grammar School in Tonbridge to open an “annexe” 10 miles away in Sevenoaks is expected in the next few weeks

Sam Freedman, head of research at Teach First and a former policy adviser to Michael Gove, suggested earlier this week that, if the plans were approved, a “raft of similar proposals” could follow.

But existing grammars have complained that they are disproportionately losing out as a result of funding being focused on the most deprived children through initiatives such as the pupil premium, one of the coalition government’s flagship policies. Paul Evans, headteacher of Colyton Grammar School in Devon, said: “I think there is a balance to be struck. I don’t think anybody has looked at what the bottom line is and asked if we have moved it too far.”

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