Grammar schools are potentially dangerous for society and should be phased out, according to a major study.

Research by academics at Durham University found grammar school students performed no better than those in non-selective state schools, once pupils' higher ability and wealth is taken into account.

The study suggested that the segregation of pupils based on academic ability was “potentially dangerous for society” and damaged social cohesion.

It found the few authorities that have retained selection and grammar schools - like Kent - have the highest level of socio-economic status segregation in England based on indicators such as free school meals.

The academics found the "apparent success" of selective schools was down to their brighter and more advantaged pupils.

They say increasing the number of schools that select pupils by ability would lead to more segregration, adding: “This kind of clustering of relative advantage is potentially dangerous for society.”

The research was based on the detailed results of nearly 550,000 pupils.

It found that once the ability and social background of pupils was taken into account, grammars were no more or less effective than other schools.

Professor Stephen Gorard, from Durham's School of Education, said: "Dividing children into the most able and the rest from an early age does not appear to lead to better results for either group.

"This means that the kind of social segregation experienced by children in selective areas in England, and the damage to social cohesion that ensues, is for no clear gain.

"This is not to decry the schools that are currently grammars, or the work of their staff. However, the findings mean that grammar schools in England endanger social cohesion for no clear improvement in overall results. The policy is a bad one."

The study comes after other claims that better-off families were at an advantage when it came to accessing grammar schools, because they could afford private tuition.

A study by Professor John Jerrim of the UCL Institute of Education revealed children who received private tutoring were five times more likely to get into grammar schools than those who did not get extra help.

Education secretary Damian Hinds recently expressed support for the idea that grammar schools should be allowed to expand.

However the government has been forced to abandon plans to allow new grammar schools to be created.