Proposals for what has been described as the first new grammar school in 50 years have been approved today.

Education Secretary Nicky Morgan has rubber stamped proposals to build the school on the old Wilderness site in Seal Hollow Road, Sevenoaks.

The 450-pupil school will technically be a new annexe of The Weald of Kent Grammar, based in Tonbridge.

Planning consent to develop the site has already been obtained.

Campaigners said they are delighted. Andrew Shilling, who together with his wife Sarah launched the campaign, said: "This is a victory for parent power, local determination and persistence.

"It has been four long years since the Knole Academy announced that it would be vacating the Wildernesse site and we therefore began lobbying Kent County Council to open a grammar school there in order to address the deep unfairness of Sevenoaks being the only district in Kent without a grammar school."

"This is a victory for parent power, local determination and persistence." - campaign group leader Andrew Shilling

But he expressed dismay that the new annexe would only be for girls.

"Whilst today’s announcement is most welcome, excluding boys from the Sevenoaks grammar annexe is very unfortunate. In recent years, Sevenoaks boys have found it harder to access grammar school places than Sevenoaks girls, and the failure of a boys' grammar school to come forward to sponsor a boys’ annexe has left Sevenoaks boys high and dry."

KCC Labour group leader Cllr Gordon Cowan said: "I am devastated. I would like to know what has changed since the former education secretary Michael Gove decided that this would be illegal. I expect this to be challenged.

"You can change legal advice but the law has not changed."

Defence secretary Michael Fallon, MP for Sevenoaks, had been among the leading Tories pressing for the plans to be approved.

He has welcomed the Department for Education’s decision to approve Weald of Kent Grammar School’s application to build an annexe in his Sevenoaks constituency.

He said: "I am very, very pleased with the decision to approve Weald of Kent Grammar School’s application to build an annexe in Sevenoaks.

"I have strongly encouraged the Minister to reach this decision, which will finally end the absurd situation of Sevenoaks being the only area in Kent not to have a grammar school. It will also help to ease the growing pressure on school places in West Kent.

"Parents will have more choice, pupils will have shorter journeys and more of them will be able to access high quality schooling on their doorstep."

MP for Tonbridge and Malling, Tom Tugendhat, has also welcomed the news. He said: “I welcome this decision which will provide an increase in school places in west Kent.

"Our schools are under great pressure and taking in an additional 90 pupils per year group will help. This development helps overcome part of this problem.

"The Weald of Kent is a fantastic school which delivers results. Its leadership and team ensure pupils get a first-rate education. I look forward to continuing to work closely with the school to help pupils achieve all they can.”

Contractors will now start work following the secretary of state's sign-off. The school expects to be able to start educating pupils at its new Sevenoaks site from September 2017.

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

A public consultation last year recorded 2,068 people in favour of the annexe and only 41 people against.

A report by The Times report said the Education Secretary was concerned refusing permission would have left the Government open to a legal challenge.

A condition of approval is that pupils at the Sevenoaks annexe spend time at the Tonbridge site once a week.

Speaking earlier this year, Mr Fallon said: “I am delighted to support this proposal from the Weald of Kent Grammar School for a satellite annexe in Sevenoaks.

“It remains deeply unfair to parents in my constituency that we are the only area in Kent not to have a grammar school. This proposal will not only go some way to eliminating this injustice, but also produce the additional places we need in west Kent."

Developer Bond Bryan is working with Kent County Council and construction partner Willmott Dixon Construction to deliver the £30m education campus.

Shadow Education Secretary Lucy Powell described the news as 'a retrograde step', adding: "So after Cameron and Nicky Morgan said I was scaremongering, they are opening new grammar schools.

"Evidence on grammar schools clear: almost entirely the preserve of the privately tutored middle-classes. Not vehicles of social mobility."

David Bower, Chair of Governors at Weald of Kent Grammar School said: “As the existing provider of education to 500 pupils from Sevenoaks we believe Weald of Kent is ideally placed to establish an annexe, offering an additional 90 places per year group.

“Recognised by Ofsted as ‘Outstanding’ we are confident in our ability to deliver the highest quality of education possible for the children in Sevenoaks and that we can extend our unique ethos to embrace students and staff across a split site operation to feel part of a single community.”

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