Schools could get little more than 150 minutes' notice before Ofsted inspectors arrive under plans for its new inspection framework, Tes can reveal.
Inspectors would then prepare at the school for a formal inspection which would start the following day.
Ofsted is understood to be keen to ensure that it has an opportunity to see schools as they really are. But the news has angered a teachers' leader who says schools should have at least 24 hours' notice before inspectors visit them.
Tes understands that the controversial new plans would see inspectors contacting a school by telephone before 10am and then arriving after 12.30pm on the same day.
Currently schools are told on the afternoon before inspectors arrive, giving them the opportunity to prepare into the night before Ofsted actually enters their school.
The new regime could make a big practical difference to heads. But it would not require Ofsted to reduce the formal notice period it gives schools, because the actual inspection will not start until following day.
Mary Bousted, National Education Union joint general secretary said: “If this is what Ofsted proposes then I think school leaders will be concerned by it.
“It is clear this pre inspection meeting will be an important conversation otherwise what would be the point of having it?.
“Given the scale of change that Ofsted is proposing with its new framework I think it is only common courtesy for school leaders to be given at least 24 hours before visiting to give them time to prepare and collect their thoughts.”
The watchdog will announce full details of its new inspection framework and begin a consultation next month.
Ofsted has said previously that it wants to give inspectors more time in schools during short inspections.
It is understood that under this proposal Ofsted's inspection team would meet the school leaders to discuss and plan the inspection a day before it takes place.
Dr Bousted said: “This comes back to the problems that Ofsted has had when it has tried to bring in no notice inspections. There is a logistical problem about whether headteachers will be there to speak to.
"I think it also shows a lack of courtesy to school leaders who should be given time to prepare and collect their thoughts rather than getting a phonecall which says ‘We are coming to your school and you need to be ready to start talking about inspection’.”
An Ofsted spokesperson said: "We are consulting on a range of proposals for the new education inspection framework. The full details will be published in January. However, we have no plans to reduce the formal notice period for school inspections.”
Nick Brook, National Association of Head Teachers deputy general secretary, said: “School leaders will not buy the line about ‘On-site preparation’. As the saying goes, ‘if it walks like a duck and quacks like a duck then it’s a duck’.
"If an inspector is in a school, reviewing documentation and speaking to staff then the inspection has already started. Inspection is routinely cited as one of the most stressful situations that a school leader will face.
"Moving to a system with only a couple of hours’ notice will send anxiety levels through the roof. It will also ruin their attempts to help other schools as many will not want to be away from their school in the year they are expecting an inspection.
“It is to be hoped that this is just a rumour. There is still a month to go before Ofsted publishes their consultation and a lot can change in that time."
Earlier this year Tes revealed that Ofsted was looking to trial no notice inspections.
Ofsted chief inspector Amanda Spielman told Tes at the time that piloting no-notice inspections was “definitely something we would like to try out”.
She was responding to a YouGov survey, published by Ofsted, in April, which found that 61 per cent of parents supported unannounced visits to schools by the education watchdog.
At the time Ms Spielman said: “We are trying to find that balance, of making sure schools aren’t completely caught on the hop, and you don’t turn up to inspect on a day where the headteacher is out of school, where the chair of governors is on holiday and where you can’t have the right conversations.
“It is balancing that with making sure you get a school as it actually operates with all of the children who are normally there so that you get a true picture of behaviour and the school culture.”
Ms Spielman was the third Ofsted chief in a row to publicly consider no-notice inspections.
In 2009, the then chief schools inspector, Christine Gilbert abandoned plans because of parental concerns that they would not be able to make their views known before an inspection.
In 2012 Sir Michael Wilshaw relented on plans for no-notice inspections after logistical concerns were raised by heads.
Instead Ofsted moved to a system where schools are told an afternoon before a visit.
Ofsted's new inspection framework being launched 2019 is also set to place much greater emphasis on the school curriculum and give less weight to exam results.