Knole Academy has opposed plans to build a new grammar annexe in Sevenoaks.

The governing body of Knole said it is "extremely concerned about the proposal" for a number of reasons.

The co-educational school, which was established as part of the government's academy programme, sent a letter to education secretary Nicky Morgan, who is currently considering the plans.

In a five page letter head teacher Mary Boyle said a new satellite facility in Sevenoaks "may subvert the success of Knole Academy's grammar-school stream and in addition, could severely skew the co-educational nature of the academy."

Mrs Boyle added: "The governing body considers that a nearby grammar school will undermine the foundations of Knole as an all-ability school - one of the key principles on which it was founded, on which it was funded, and on which the sponsors and governors are pleased to support."

She claims Knole asked the Weald of Kent Grammar in September to provide details of the size of the annexe proposed as a matter of urgency but have had no reply.

"There are appears to be a lack of clarity as to what would happen to boys in this proposal. As it is the case that if operating under a selective system, there is a small lack of grammar places around Sevenoaks for boys and a small lack of places in Tonbridge and Tunbridge Wells for girls.

"It is difficult to understand why this particular proposal has been put forward since it does not meet the needs of the area," Mrs Boyle continued.

Knole's governing body also believes there has been inadequate consultation on the matter.

The application is currently being considered by Nicky Morgan and contractors are ready to start work, subject to the secretary of state's sign-off.

While it is illegal to build new grammar schools in the UK, the government encourages successful schools to expand, meaning it would be possible to open an annexe.