In a letter to the Audit Commission's director of best value inspection Wendy Thomson, Mr Sparke says inspectors' final reports contain factual errors even though they had been pointed out at earlier stages. He says inspectors repeatedly ask for copies of the same corporate and policy documents.
Mr Sparke criticises inspectors for carrying out separate interviews with councillors, senior officers and the chief executive for each inspection.
The letter says: 'Several leading members of my authority have now made it clear they are no longer prepared to be interviewed by your inspectors and I cannot blame them for it.'
He says inspectors widen their remit without notice and suggest more resources should be used to improve services, ignoring the council's spending limitations.
The letter concludes: 'Your inspection process is flawed, subjective, ineffective and damaging, and it is not value for money.'
Mr Sparke says inspectors are inexperienced, lack credibility and fail to define their criteria in advance of an inspection. Dr Thomson said: 'There is a delicate balance between operating a framework that judgments can be made within and so risking criticism, or alternatively be accused of over prescribing standards rather than protecting local discretion and democracy.'
She said the commission is keen to develop a constructive dialogue with councils and added that a recent market research report showed nearly 80% of council staff said inspectors behaved professionally at all times while carrying out an inspection.