Maidstone Grammar School for Girls (MGGS) operated an unlawful admissions policy for prospective sixth form students, the Local Government Ombudsman has found.

The school in Buckland Road requires pupils to have six GCSEs at grade A* to C, including at least four B grades as well as B grades in the subjects they are taking at A-level.

But it was also found to actually be making offers to external students based on a more rigorous points-based system.

The revelation comes after MGGS head Deborah Stanley strenuously denied employing unethical tactics to ensure the best A-level grades in January.

The watchdog began investigating after a complaint from a parent of a student refused a conditional offer on the basis of the unpublished criteria, despite meeting the school’s minimum requirements.

The inspector found MGGS wasn't following its own admission policies and breached the statutory guidance which states schools must clearly set out how they will admit children.

The report states: “The School did not follow its published admission arrangements when making conditional offers to applicants for September 2016 entry. It used an additional oversubscription criterion, which was not mentioned in the arrangements and had not been subject to consultation."

“Using an APS (points based system) to rank applicants based on academic ability contradicted the published oversubscription criteria, which apply to all external applicants with the minimum academic requirements, giving priority to looked after children, siblings, students with health issues and finally those living closest.”

"The School did not follow its published admission arrangements when making conditional offers to applicants for September 2016 entry" - Local Government Ombudsman

They were also critical of how Kent County Council’s independent panel arbitrated the dispute and did not challenge the school’s policies.

They will receive retraining.

The school has agreed to drop the use of the points-based system, apologise to the family and pay £250 in compensation.

The Ombudsman found the loss of a school place did not itself constitute an injustice but the confusion caused by the fault of the school and panel did.

Deborah Stanley, headteacher, said: “The Ombudsman specifically said that the pupil’s ‘grades were lower than predicted and he did not meet the subject requirements for his original A Level choices, or the revised choices put forward by Mr A (the father). So, even if the school had made a conditional offer, it would not have followed this with a firm offer’.

“However, we no longer include the average points score in our admissions criteria and also agreed with the Ombudsman’s recommendation of a £250 donation to the family, because of the uncertainty and confusion caused.”

The decision comes after county education chiefs said they would not investigate whether schools are ejecting sixth forth students because of poor performance.

It follows the news a grammar school in Bromley, St Olave's, was facing the threat of legal action from a group of parents contesting the exclusion of their children who had not done well in their AS exams in Year 12.

Invicta Girls Grammar have faced similar complaints in the past but have always denied any wrongdoing.