A state-school campaign group wants Ofsted to make reports on schools that convert into academies to become accessible “in perpetuity”, rather than removing them from its website after five years.

Schools that become academies after December 2013 have previous Ofsted reports wiped from the web five years after they convert. For those that converted before then, the window is just three years.

The Local Schools Network is concerned the rule means “history can be erased”.

“You need to be able to see how schools have changed over the years,” said Janet Downs, a representative. “People make remarks about how schools were as part of their marketing, and it’s important to be able to check.”

Ofsted labels schools that become academies as having closed, so their inspection history starts afresh. Past reports are linked to the new school on the inspectorate’s website through a tab labelled “related providers”.

However, these reports are deleted after five years, effectively erasing a new academy’s backstory.

You need to be able to see how schools have changed over the years

Academies transferring between sponsors are also granted three years’ respite from further inspections.

Professor Colin Richards, a former senior Ofsted inspector, told Schools Week the rules were unfair.

“I strongly believe that as a matter of natural justice the same rules should apply to all schools including academies,” he said.

“Each of their inspection histories should be publicly available. Why should academies have their records wiped clean?”

In July, Schools Week found the ratings of 718 schools had been wiped clean after becoming an academy or rebrokering. We estimate these schools are teaching more than 300,000 young people – or about four per cent of the 8.67 million pupils who attend England’s schools.

Downs described the system of hidden reports for some schools as “a mess”.

“The reports should be there to check, whether they are predecessor schools or not, because people make claims and these claims need to be verified,” she said.

Barry Smith, the new principal of Great Yarmouth Charter Academy in Norfolk, apologised last month after he made comments in a local newspaper that the school had once been like a “war zone”.

The school’s former headteacher, Ivan Pegg, said the remarks were “very unfair”. An inspection report from 2005, still available on Ofsted’s website, shows the school was rated ‘good’ at one time.

Downs said the incident highlights how important it is for a school’s past to remain available: “It’s important the data remains accessible so there are facts to rely on.”

Historical analysis of Ofsted reports also enabled Schools Week to catch a “copy-and-paste” inspector in 2014.

David Marshall, an inspector hired by Ofsted from a third-party contractor, repeatedly used the same paragraphs throughout his reports for several years. If the reports were not available across the timeframe, this repetition would never have been discovered.

Ofsted said the policy has existed since 2010 for any school that counts as ‘closed’.