Ofsted says it has found no evidence that three academies in Norfolk were given improper advance warning about the dates of their inspections.

The watchdog has completed an investigation into allegations made in the Observer that the schools had been tipped off about when they could expect inspectors to arrive, leaving them with an unfair advantage over other schools.

It looked into whether Great Yarmouth Primary, Ormiston Academy and Thetford Academy were given advance notice of their inspection dates; if the right processes are in place and properly enforced to keep Ofsted’s inspection timetable protected; and whether any lessons can be learned for future practice.

Led by Ofsted’s director of quality and training Sir Robin Bosher, the investigation could not find evidence to back up the allegations. Instead, it found that the practice among the trust’s schools of remaining on a high level of inspection readiness for fairly long periods had led people to believe it might have had prior knowledge of inspections.

However, it did find that the chief executive of the Inspiration Trust to which Great Yarmouth Primary Academy belongs, Dame Rachel de Souza, was accidentally sent information which included the date of that school’s inspection.

Dame Rachel was training to become a seconded inspector at the time and was accidentally provided with a copy of the inspection schedule. Once the mistake came to light, it says the schedule was altered to change the date of the academy’s inspection.

“Sir Robin Bosher’s report utterly refutes allegations of irregularities about Ofsted inspections of two of our schools, and a third school where our Chief Executive was Executive Principal at the time,” said a spokesperson for the Inspiration Trust.

“We maintain the highest levels of integrity and transparency at our schools. This report underlines that.”

As a result of the investigation, Sir Robin is recommending that Ofsted should look at what additional procedures might be needed to bolster existing controls to protect confidentiality and prevent conflicts of interest.

In addition, he has suggested that Ofsted looks at a more “flexible” approach to timings that would make it less predictable when inspections might occur.