A test provider has "admitted" there is no evidence that the controversial 11-Plus test is “tutor-proof”, according to a campaign group which has branded it a “legalised form of discrimination”.

This month, thousands of children across Bucks sat the 11-Plus, which was introduced to the county in 2013 with the Centre for Evaluation and Monitoring (CEM) and grammar schools around the area saying the new test would be “fairer” because it was “resistant to coaching”.

According to campaign group Local Equal Excellent (LEE), this is not the case.

It said in an email responding to a Freedom of Information (FOI) request, CEM stated: “Without extensive and expensive research, it is not possible to quantify the impact of coaching on the results from our tests, since we currently have no access to information regarding the levels of coaching that children have received.”

Campaigners said this meant CEM had “conceded” it had no evidence that the 11-Plus test is, as claimed, resistant to coaching, and are now calling for the test to be scrapped.

LEE spokesman Rebecca Hickman said: “There isn’t a shred of evidence that the 11 plus is resistant to coaching.

"And if the test is unfair, the system is unfair.

“Given the overwhelming evidence that the test disadvantages children from certain backgrounds, it seems indefensible not to withdraw it immediately.

“Instead the grammar schools are choosing to keep reproducing the unfairness.”

It comes after a survey found teachers and school leaders were overwhelmingly opposed to Theresa May’s controversial plans for a new wave of grammar schools, which could see Marlow’s Sir William Borlase's expanded into her Maidenhead constituency.

According to the LEE, more than 8,000 children sit the 11-Plus test every year, however in 2014, only 10 children on free school meals passed the test.

It also said the pass rate for pupils at private schools is around 60 per cent compared to 22 per cent for state school pupils, and the pass rate for children from the wealthier districts of the county is around twice the pass rate of the poorer districts.

Rafiq Raja, chairman of the Muslim Parents Association, said: “As things stand the 11-Plus is a legalised form of discrimination.

“There is no real effort being made to understand its far-reaching consequences for certain sections of the community; as a result the attainment gap in Bucks is one of the largest in the country.

“We need an education system in Bucks that works for everyone, not just the privileged few.”

Professor Rob Coe, CEM director at Durham University, said: “We aim to make our entrance assessments as fair as possible.

"Our entrance assessments draw on research identifying the best predictors of later achievement, and are designed to enable all children to demonstrate their academic potential without excessive preparation.”