Ofsted's school inspections have been reduced to "tick-box" exercises and the watchdog's wider children's remit leaves it vulnerable to "unexploded bombs" in social care, a group of former chief inspectors warned this week.
Sir Mike Tomlinson, chief schools inspector from 2000-02, told MPs the school inspections framework had been overloaded by politicians' whims, leaving Ofsted too little time to properly inspect schools' core work. He added that the framework had become "tick-box", with a "potential overuse of data".
Lord Sutherland, another of a trio of former chief schools inspectors who appeared before the Commons education select committee on Wednesday, said he was "disappointed" Ofsted had "grown so big" by taking on children's social care.
"It may be a mistake to put childcare under them (Ofsted) because there are a lot of unexploded bombs there," he said. "If they go off - and they might - Ofsted's reputation will suffer."
The comments come as ministers prepare proposals to radically reform the watchdog, simplifying its inspections regime.
Lord Sutherland, chief inspector from 1992-94, when Ofsted was first created, said it had been a mistake to give the watchdog a wider remit. "I am disappointed that these additional responsibilities have been given to Ofsted."
Sir Mike added that the policy of having "limiting judgments" that restricted school verdicts if they fell down in particular areas had not been "a good innovation".
Maurice Smith, chief inspector in 2006, said: "If there is something you particularly want to happen in the education system in this country, then get it in the inspection framework because it will happen."
An Ofsted spokeswoman said its inspection framework was the result of detailed consultation and "reflects the right balance of judgements for the time".
Bringing education and care services under the same inspectorate had allowed Ofsted to check that services were joined up, and it had shown it was still possible to carry out "high-quality" inspections, she said. She added that limiting judgments were right for some elements of schools' performance.