Ofsted has vowed to press ahead with trials of no-notice inspections, despite overwhelming criticism of the proposal by school staff.

Over three-quarters of heads said they either disagreed or strongly disagreed with the idea of unannounced inspections, results from an Ofsted consultation show.

More than seven out of ten teachers also said they were against such inspections, saying they showed a lack of trust, were impractical and would increase stress on staff.

Their criticism comes in response to a wide range of proposed changes to the inspection regime from September 2009, which will also include halving the frequency of inspections for high-performing schools.

Concerns about no-notice inspections, also dubbed “dawn-raids”, follow comments made by Aspect, the union representing the majority of school inspectors, that zero-notice inspections would cause problems in securing time with senior teachers.

But Christine Gilbert, the chief inspector, has refused to drop the idea. Trials will now begin this term, as Ms Gilbert weighs up whether to extend the idea to all schools from next September.

Ofsted said the zero-notice approach was popular with parents and carers. Seven out of ten said they supported the idea, according to the consultation results.

But parents and carers accounted for only 5 per cent of the 1,666 respondents. Ofsted said despite the small number, it believed the view was representative of parents more widely.

“I’m disappointed they are going through with this,” said John Dunford, general secretary of the Association of School and College Leaders. “They should have realised that the no-notice idea is a non-starter.

“I hope the evidence they get from the trials persuades Ofsted that no- notice will fail to give them the information they want.”

Dr Dunford said that no-notice “harked back” to the old inspection regime, in which school self-evaluation did not form a central part of inspections.

In other parts of the consultation, Ofsted said it would continue with plans to increase the time between inspections for good and outstanding schools from once every three years to once every six years.

The proposal won strong support from school staff, with three-quarters of heads backing the idea, but was opposed by almost half of parents.

Ofsted said it was still “minded” to adopt the proposal, although it will consider a gap of five years between inspections after concerns were raised that standards could slip.

Satisfactory schools can expect more monitoring visits, despite fears that it could put too much pressure on staff and make it difficult for schools to recruit.

Pilot inspections over the next two terms will also increase the amount of time spent observing lessons, as Ofsted focuses more on the achievement of different groups of pupils, including vulnerable, ethnic minority and gifted children.

One criticism of the current light-touch regime has been that insufficient time is spent watching lessons in action.

Controversial proposals to introduce a minimum exam benchmark for schools will also be taken forward and trialled.

Ms Gilbert has previously suggested that if schools do not hit certain targets - for example, 30 per cent of pupils achieving five good GCSEs including English and maths - they could not receive a grading above satisfactory.

In the consultation, only 46 per cent of respondents were in favour of the approach, with 37 per cent against.

The commonest complaints were that a “one-size-fits-all” approach would be unfair to those schools that were working in the most challenging circumstances, and that value-added scores needed to be taken into account.

New tests will also be developed to judge schools on their capacity to improve.

This could include paying greater attention to the quality of leadership in different areas of the school and its track record of improvement, Ofsted said.