The recommendation from an influential committee of MPs to split Ofsted's responsibilities for education and children's care has been described as "absolute baloney" by the watchdog's former chair.
Zenna Atkins, who oversaw the expansion of Ofsted between 2006 and 2010, said the education select committee members had "completely missed the point".
Following an investigation into Ofsted's role and performance, the committee called for it to be divided into two distinct inspectorates, covering education and children's care.
"An organisation doesn't become too big to manage," she told The TES. "The things we introduced had never happened before. It's completely false to say one organisation can't do these things.
"There has been noticeably, markedly and without question an improvement. We saved #163;80 million, year on year. In the current fiscal climate it would be financially ridiculous to separate (Ofsted)."
The committee argued that too few inspectors have "recent and relevant" front-line experience, but said there was no "systemic difference in quality" between Her Majesty's Inspectors and contracted inspectors.
The MPs also said that unannounced inspections were "the preferable model". The committee called for a "stuck" grade for schools that have been persistently graded satisfactory, and two new posts - a chief education officer and chief children's care officer - in the Department for Education to improve its communication with Ofsted.
Chief inspector Christine Gilbert said: "There are many constructive suggestions and observations contained in the report and we will now consider these in detail."