school exam
Admissions for grammar schools are decided by the 11-plus exam Getty

Britain is set to get its first grammar school in 50 years after the idea was given the green light by education secretary Nicky Morgan, say reports. Morgan approved plans to expand a new 450-pupil school in Sevenoaks in Kent after months of battling between campaigners and ministers, reported The Times.

Labour introduced a law banning new taxpayer-funded grammar schools – which select pupils on the basis of academic ability – while in power in 1998. The approved school in Sevenoaks gets around this ban as it is an expansion of the Weald of Kent Grammar School in Tonbridge.

Morgan insists the approval does not mean the government is planning to scrap the law on building new grammar schools, also known as selective state schools, but Labour's shadow chancellor Lucy Powell said the decision will "open up the floodgates" for further applications.

As part of the conditions for the approval of the expansion, pupils at the new Sevenoaks school will be required to spend some time at the Tonbridge site once a week.

There is an argument that the approval process for grammar schools – where pupils are selected at the age of 11 through examination – favours children from wealthier background who have access to private tuition.

Ofsted chief inspector Sir Michael Wilshaw, a former state secondary school head teacher, previously told the Observer: "Grammar schools are stuffed full of middle-class kids. A tiny percentage are on free school meals: 3%. That is a nonsense. Anyone who thinks grammar schools are going to increase social mobility needs to look at those figures. I don't think they work."

However, London mayor Boris Johnson described the decline of the grammar schools in the British education system as a ''tragedy'', with prime minster David Cameron adding "all good schools" should have the right to expand, including grammars.

The move was also backed by Paul Carter, Tory leader of Kent county council. He told the Times: "The school took great effort to submit their bid to give greater detailed information on how it will be one school, not two schools, and they did a very good job on that."

He added: "The big issue about this decision is that it won't open up the floodgates. You have to have a grammar school there in the first place to expand. If you can't expand on site you have to expand elsewhere, and that's all we have done in this case."

Sarah Shilling, a mother of three who has campaigned for the grammar school in Sevenoaks for the past four years, added: "We have got children from Sevenoaks passing the [11-plus] exam in Kent and there is no school for them to go to. There is a growing population and all the non-selective schools are allowed to expand and all the church schools. The selective schools need to expand as well to reflect that."