Sir Michael Wilshaw, the new head of Ofsted, the education standards watchdog, blamed the headteachers for unacceptably high levels of poor instruction in schools. He said he wanted "less tolerance of poor leadership" and a "no excuses" culture towards poor performance in schools. He added that heads were to blame for the "national disaster" of thousands of newly trained teachers quitting the job soon after starting in the classroom.

His comments were based on Ofsted statistics showing that 24 per cent of school leaders had not been ranked as "good" as a result of school inspections – one per cent were inadequate and 23 per cent were satisfactory.

Sir Michael, who ran a highly successful academy – Mossbourne in Hackney, east London – before taking on the post of chief schools inspector last month, said he intended to target 3,000 schools that he described as "coasting" with satisfactory ratings in each of their last two reports. He has announced his intention of abolishing the rating "satisfactory" and replacing it with "requires improvement".

However, Russell Hobby, general secretary of the National Association of Head Teachers, warned that the "constant denigration" of heads and teachers would lead to many quitting. "I don't know of any other profession where 76 per cent of its leaders are acknowledged to be good," he said. "It's the spin that's put on the figures." He said he had spent the weekend at a conference of 150 headteachers, many of whom had been "outraged" at the inspector's comments.