Mary Wilkinson, the editor from 1983 until her retirement in March last year, alleged that the former chief, who resigned earlier this month, wanted to prevent the publication of articles that were critical of Scope.
In 2004, the magazine included a postcard campaign by the Voluntary Euthanasia Society, now Dignity in Dying, that Manwaring felt ran contrary to Scope's policy. He published a statement in the magazine disassociating himself from it.
Wilkinson said: "That the magazine used to be independent was a credit to Scope. It would be great to see that editorial independence restored."
Louis High, head of communications at Scope, said Manwaring's departure did not detract from business as usual, "and this includes the management and publishing of Disability Now".