In written evidence presented this week, Greg Wilkinson said he spoke as 'a critical friend in the hope that it will make a valuable organisation even better'.
But Mr Wilkinson, who resigned as the Audit Commission's associate director of local government studies last July, challenges Ofsted's methodology, efficiency neutrality and accountability.
Questioning why an inspection aimed at judging the performance of an LEA spends more than half its time in individual schools, Mr Wilkinson says this leaves inspectors open to allegations that such visits 'are little more than fishing expeditions in which inspectors pick up gossip about the LEA'.
'Key conclusions in inspection reports are often supported by a weak evidence base. For example, critical judgments on LEAs' overall performance have been formed on the basis of views expressed by heads or teachers at one or two schools,' he says.
Mr Wilkinson, who works as a consultant and is the councillor with prime responsibility for education at Hammersmith and Fulham LBC, also criticises Ofsted for not giving LEAs adequate time to influence inspection reports, which contain bland, unhelpful recommendations and which are written in 'an essayistic and on occasions journalistic style'.
'Particularly in the commentaries, the writers expend considerable effort on crafting certain criticisms in a lively or colourful style, rather than on the clear exposition of problems and solutions. Some of these literary flourishes create antagonism between the inspectors and the LEA and impede discussion of the substantive issues,' he says.
Unlike the Audit Commission and other inspectorates Ofsted is not accountable to any board, he says. This means LEAs 'have reason to question its methods, behaviour, objectivity and fairness'.
The Local Government Association told the inquiry an advisory panel should be set up to have a say in the appointment of the Ofsted chief inspector.
But LGA education director Neil Fletcher said: 'What's important is whether an authority or a school is doing a good job or not.'