A new category of "coasting" schools will be created for those whose exam results are satisfactory but who could do better, the Office for Standards in Education said yesterday.
Officials from the office suggested that as many as 3,500 schools, including some highly selective ones, may be attacked for complacency.
Coasting schools will have to produce an action plan and will receive regular follow-up visits from inspectors in exactly the same way as schools which are classified as failing.
Estelle Morris, the school standards minister, said: "We now have the information based on exam results and inspections which enables us to spot with confidence those schools. There is no room for complacency even amongst schools which appear to be getting reasonable results."
Chris Woodhead, the Chief Inspector of Schools, said: "Our very tentative feel for the size of the problem is that coasting schools could represent between 10 and 15 per cent of all the schools."
The changes are part of a new inspection regime, to be introduced from 2000, which will mean there will be more inspections for poor schools and fewer for the good ones.
A consultation paper suggests between 20 and 30 per cent of schools may not need further detailed inspections.
Routine inspections for all schools will take place once every five or six years instead of the present four, but inspectors will visit the worst schools every two years.
Schools which qualify for new "light-touch" inspections will have to show that they have very good exam results compared with similar schools and in relation to the national average, have a faster-than-average improvement rate and also excellent previous inspection reports.
These inspections will be shorter than the present ones and inspectors will not necessarily see all teachers.
Mr Woodhead said the new arrangements were in accordance with the Government's belief of "intervention in direct proportion to success" but the criteria for "light-touch" inspections must be demanding. He added:"Good schools have demonstrated that they can manage their own destinies and further checks ought to be as light as they can be."
The paper also proposes that schools should receive only between four and eight weeks' notice of inspectors' visits compared, with the present two terms.
It argues that this would reduce stress for teachers awaiting an inspection.
n A leading academic yesterday launched a scathing attack on the inspectorate, telling MPs Ofsted was amateurish and inaccurate, with no sound research basis for its findings.
Schools should be subject to random spot-checks, Professor Carol Fitz- Gibbon, of the University of Durham, told the Commons Education Select Committee. She said that Ofsted was misleading parents and wasting teachers' time by providing inaccurate and subjective information.
She said: "It's inaccurate. If you give people inaccurate information they will make the wrong decisions and emphasise areas which are not the problem at all.
"They are diverted into producing development plans and action plans on the basis of poor evidence. They cannot evaluate what the schools are doing better than the schools themselves, and are giving bad value for money."
Professor Fitz-Gibbon is a leading expert on "value-added" analysis, which monitors schools by measuring the progress of individual pupils.
One in four schools use Professor Fitz-Gibbon's analysis of results to help raise standards.
She said: "It is Ofsted's job to show us that their judgements are correct, but there are no studies showing that."