Ofsted’s proposed report cards will make it more difficult to tackle the reliability of inspections and they could be “harder” for parents to use, a former Government adviser has warned.

Sam Freedman, who worked at the Department for Education (DfE) as a policy adviser to former education secretary Michael Gove, said he had “a lot of worries” about the proposals.

Mr Freedman, a senior fellow at the Institute for Government, told MPs that the previous system of headline Ofsted grades for overall effectiveness for schools had been “helpful” for parents.

His comments came after the Education Secretary rejected criticism of plans to revamp Ofsted’s grading system for schools in England with a new “report card-style” scale.

On Monday, Bridget Phillipson said she “fundamentally” rejected the idea that giving more information on where schools need to improve is “not something that parents want”, after education unions and the sister of a headteacher who took her own life following an inspection criticised the plans.

Schools in England could be graded across a variety of different areas – including attendance and inclusion – using a colour-coded five-point scale.

During an education select committee, Mr Freedman said Ofsted’s problem has been “reliability of assessments” and the proposed system of lots of graded sub judgments makes this “harder”.

The Government announced last year that headline Ofsted grades for overall effectiveness for schools in England would be scrapped.

Previously, Ofsted awarded one of four single-phrase inspection judgments: outstanding, good, requires improvement and inadequate.

Now schools in England would receive gradings – from the red-coloured “causing concern” to orange-coloured “attention needed”, through the green shades of “secure”, “strong” and “exemplary” – for at least eight areas of a school’s provision under the new proposals.

Mr Freedman told MPs on Tuesday: “I’m worried that this makes it harder for Ofsted to tackle its real issue which is reliability and consistency of inspection and doesn’t actually deal with any of the concerns that schools have, and possibly makes it harder for parents to use them as well.

“So I have quite a lot of worries about this new model.”

He added: “I don’t think the problem with the previous model was that we had single word judgments and a single overarching judgment. I think that was actually quite helpful for parents.”

Education Secretary Bridget Phillipson speaking at the Centre For Social Justice on Monday (Lucy North/PA)

The reforms follow criticism of the inspection system following the death of headteacher Ruth Perry who took her own life after an Ofsted report downgraded her Caversham Primary School in Reading from the highest to the lowest overall effectiveness rating.

During the committee on Tuesday, Daniel Kebede, general secretary of the National Education Union (NEU), said: “We now have eight areas of measurement, (a) five-scale grade, that’s 40 potential areas of judgment.

“Ofsted were tasked with bringing about a system of inspection that reduced pressure on the school system in quite tragic circumstances. It’s our view that this will make things worse, not better.

“We’ve all got a shared challenge in regards to the crisis in recruitment and retention – Ofsted included. It’s our fear that this will drive more teachers and school leaders out of the profession.”