Ofsted has warned that the “outstanding” grade has been devalued for some parents because inspectors are not able to routinely check on top-rated schools.

HMI Dan Lambert said that many parents, teachers, leaders and governors feel that outstanding schools being exempt from inspection is not in the school or pupils’ best interest.

And he said that Ofsted was concerned that schools with a lower inspection grade could be providing a better standard of education than one rated as outstanding.

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He said that in some cases he has written to parents to say that “as the law stands Ofsted has no firm plans to inspect their child’s school, ever”.

It was revealed last year that 1,620 schools had not been inspected for six years or more, including 296 schools that had not been inspected for 10 years.

Outstanding schools have been exempt from routine inspection since 2012 but inspectors can go in where concerns are raised about standards or safeguarding. 

Writing on in a new Ofsted blog, Mr Lambert said: “For some parents, the top inspection grade has been devalued.

“For Ofsted’s part, we believe that the exemption has had its day and the time is ripe for the Department for Education to revisit the policy.”

He added: “Amanda Spielman, Ofsted’s Chief Inspector, sparked interest from the media when she told the education select committee that some schools have not been inspected in 10 years. Some pointed the finger at Ofsted. I can see why. However, many people did not realise that this is exactly how it is set out in law.

“Ofsted has no legal basis to include these schools in our cycle of routine inspections. This is difficult for many to understand. Indeed, I have found myself writing to parents to say that, as the law stands, we have no firm plans to inspect their child’s school, ever.”

Mr Lambert also suggests that leaders of outstanding schools can value being inspected after a long wait.

He added: “I find the inspection of outstanding schools to be some of the most enjoyable work I do. Often, leaders have been waiting a long time for their inspection. It offers them the chance to show and share the strengths of their school and hold professional, developmental discussions about what areas they need to address.”

Ofsted revealed earlier this week that fewer than one in five parents realise that “outstanding” schools are exempt from routine reinspection.

The figures from the inspectorate’s fourth annual survey, show that only 17 per cent of parents were aware that schools given the top inspection grade are not routinely revisited by Ofsted.

Almost three-quarters of parents surveyed said that “outstanding” schools should be inspected as often as those rated “good.”

Schools standards minister Nick Gibb told the inspectorate last year to inspect at least 10 per cent of “outstanding” schools.

It was revealed in March that less than a quarter of the “outstanding” schools inspected by Ofsted in the first term of this school year kept their top grade.