An investigation has been launched after a school that was told it needs to improve complained that it feels “let down” by the “flawed” Ofsted inspection process.

The Meridian School in Royston was visited by Ofsted in October, with inspectors spending two days observing lessons. After receiving feedback from the inspectors that more than 80 per cent of their teaching was outstanding or good, staff the found out that the school had been given an overall rating of “requires improvement.”

They have made a formal complaint to Ofsted and Serco, the contractor which employs the inspectors, both of whom are investigating the conflict between the report and the overall score.

Dr Michael Firth, headteacher of The Meridian School, said: “Our view is that the report is deeply flawed because they haven’t based it on the evidence they collected or the procedures they are meant to follow. A lot of assumptions have been made which aren’t backed up by their findings from the inspection.

“We are committed to the Ofsted inspection system, and will accept criticism if it is justified, but we feel hugely let down by a process which should be a process for good.”

The school believes that the “requires improvement” rating was given due to the underperformance of a group of 10-15 high-achieving students, who didn’t make the progress they were supposed to in English

Kim Horner, deputy head at Meridian, said: “At the end of the first day the inspectors didn’t raise any major issues. In fact their feedback reflected our evaluation, which was that at least 86 per cent of teaching was graded good or outstanding. Then the report came back with something completely different. If there was a problem with our English grades they should have raised it then, as the data has been available online since February.

“It feels like a templated report –because of this small group of figures we fit into a certain template despite all the evidence that says otherwise.”

Inspectors last visited Meridian in 2010, when the school received a good rating. Since then the Ofsted inspection framework has changed, making it harder for schools to achieve high scores.

In 2013, English GCSE pass rates at the school rose to 74 per cent compared to 72 per cent in 2012. Maths GCSE passes also rose from 68 per cent to 80 per cent in the same time period.

The result of Meridian’s appeal is expected by the end of November.

A spokesman for Ofsted said they could not comment on individual cases.