The author of a review into the care of people with learning disabilities in England has reported an "absence of any tangible progress" since he issued it.
Sir Stephen Bubb headed the review which was prompted by the Winterbourne View care home abuse scandal in 2011.
His analysis, published in November, urged the closure of some in-patient facilities and more community services.
England's chief nursing officer said improvements must be made "at a fast but safe pace".
Neglect and abuse of patients by staff at Winterbourne View, a private residential hospital near Bristol, was uncovered by BBC Panorama. Six people were jailed in 2012 and five given suspended sentences.
Sir Stephen said that although the number of people being discharged from Winterbourne-style institutions was now greater than those being admitted, "it remains abundantly clear that a revolving door of discharges and admissions will continue unless a closure and transition programme is acted on".
He said although NHS England had made it a "top strategic objective" to improve conditions for people with learning disabilities, "the pace of change remains slow, and this is unacceptable".
Sir Stephen, who is chief executive of the Association of Chief Executives of Voluntary Organisations (ACEVO), said there appeared to be "no dialogue" between NHS England and third sector providers, such as charities and community organisations, about how to deliver the transition.
He said this six-month review should be treated as a "warning call" ahead of a "formal stock take of actions" in a further six months' time.