Ofsted's chief inspector has admitted she is anxious about the decision to exempt outstanding schools from routine inspections, in comments that could embarrass the Government.
Christine Gilbert has also hinted that the move could be down to the need to save money.
Her comments have prompted allegations from shadow education secretary Andy Burnham of "cost-cutting" at the expense of teaching standards.
Inspectors now have to rely on "desktop" data analysis to alert them to any deterioration in schools rated outstanding.
When asked at a Commons select committee meeting looking into Ofsted's role and performance about the decision to stop inspecting outstanding schools every five years, Ms Gilbert said: "I have some anxiety about not inspecting those schools routinely ... At the same time, I accept - resources being what they are - that there is logic in what is going on now."
When he announced in May 2010 that outstanding schools would be exempt from inspections, education secretary Michael Gove told The TES that making schools "free of that burden" would allow Ofsted to "more effectively focus" inspectors' work.
Ms Gilbert, who is due to leave the watchdog in October, said some outstanding schools would be inspected as part of Ofsted's subject surveys, and added that complaints from parents and a "risk analysis" of schools' data would flag up problems.
"Essentially it will be a desktop analysis of all outstanding schools, as we have done this year," she said. "If the pattern is giving rise to a number of questions and it looks as though there has been a deterioration of performance, we will go in and inspect."
But the policy has received widespread criticism. Mr Burnham said: "We want to reduce burdens on heads and teachers, and inspections should be proportionate - outstanding schools have earned more autonomy.
"But schools do change, and sometimes quickly, which is why any 'risk analysis' must be robust enough to highlight problems.
"Changes to Ofsted procedures should be driven by a thorough look at the best way to raise standards for all children, not simply by cost-cutting."
Russell Hobby, general secretary of heads' union the NAHT, said: "Although our members in outstanding schools probably won't thank me for saying it, I too am uncomfortable with no inspections for outstanding schools.
"The key question is: would an inspection help us improve or tell us things we don't already know? If the answer is no, then it is just a burden. The answer lies in better inspection for all schools more than exemption for some."
At the Parkside Federation in Cambridge, executive principal Andrew Hutchinson has to cope with inspections at its satisfactory-rated Coleridge campus but not at its Parkside site, graded outstanding by Ofsted. He has decided to bring in external experts to scrutinise performance at Parkside.
"Not having Ofsted inspections leaves a gap if the school is never looked at from the outside, and that is a recipe for potential problems," Mr Hutchinson said.
Janet Tomlinson, managing director of inspections at independent service provider Tribal, said it was vital to ensure outstanding schools "don't slip through the net", warning that inspectors' "standards may start to slip" if they no longer visit the best schools.
A Department for Education spokesman said: "If serious concerns are raised either by parents or by performance data, Ofsted will be able to carry out a full inspection."