Mr Best, chief executive for five years, has been temporarily succeeded by Kate Page, formerly corporate director of neighbourhood services.
Leader Isobel McCall (Lib Dem) said: “John has been an extremely dedicated and enthusiastic chief executive.”
The report was commissioned by Ms McCall from consultant Richard Penn after design and cost overrun problems arose.
Mr Penn said: “The question has to be asked as to why the chief executive, regardless of personal style preference, did not see it as his clear organisational responsibility to intervene, and to intervene decisively, when he became aware there were organisational obstacles to the achievement of [this] key aspect of the council’s agenda.”
Mr Best said: “I am tremendously grateful for the opportunity to have led the council at such a critical and exciting time in its evolution.”