Phil Purcell, facing calls for his replacement as chairman and chief executive of Morgan Stanley, has hit out at critics he claims are risking damage to the Wall Street bank's business.

Mr Purcell said in a memo to staff that the "Sturm und Drang" generated by the media campaign against him being waged by eight former executives was making it difficult to explain the management shake-up that has brought his leadership to a crisis.

"I do not believe it is in the custom of Morgan Stanley for any member of this firm - current or past - to risk a course of action that would damage our franchise."

In the letter Mr Purcell admits he is facing internal opposition to last week's reshuffle, which led to the departure of three senior executives. He insisted the changes were in the best interests of staff, clients and shareholders, but added: "I know some of you are not quite convinced."

Bob Scott, one of the former Morgan Stanley executives leading the campaign against Mr Purcell, yesterday defended their decision to make their criticisms public. He said the group sent a private letter to Morgan Stanley's board expressing their concerns about Mr Purcell and their fear that he could react to the challenge to his leadership by removing more senior executives. "The only answer we received to that letter was for Phil to act out our worst fears by retaliating against very senior people in the firm. Only then did we make our concerns public."