Dresdner said in a statement that Mr Robertson's departure, which was by mutual consent, was due to "different views on the strategic and organisational direction of the investment banking activities of the Dresdner Bank group".
He is being replaced as chairman by Lord Walker, who has been part of the Dresdner group since 1991 as chairman of the London-based asset management group Thornton & Co.
The investment bank's executive committee will now be chaired by Hansgeorg Hofmann, deputy chairman of Kleinwort Benson group.
In a statement issued simultaneously in Britain and Germany, the chairman of Dresdner group, Juergen Sarrazin, said: "All of us are agreed that, to recognise the full potential of Dresdner Kleinwort Benson, we must fully integrate our resources in London and Frankfurt, so that they and all our offices operate as one entity. Sadly, we have differed with Simon about the way this is best achieved.
"We deeply regret the departure of Simon. He has made a very significant contribution to Kleinwort Benson and the successful creation of Dresdner Kleinwort Benson, our global investment banking business."
Mr Robertson, 55, joined Kleinwort in 1963.
A spokeswoman for Dresdner said last night: "The disagreement was basically about how we should go forward in managing the integration process. The two views were irreconcilable.
"Simon Robertson felt that the whole investment banking operation should be managed out of London. We felt we were trying to build up a global banking business."
The spokeswoman said Dresdner believed that centring the business in London would be too narrow a focus from which to develop a global business.
When Dresdner acquired Kleinwort Benson in June 1995 it brought with it investment banking skills in the derivative and financing operations, the spokeswoman said. The difficulties arose in trying to find a management structure which was suitable not only for incorporating the skills already in place in London but also the global investment banking skills.
There are four basic pillars to Kleinwort's investment banking interests - equities, finance, markets and corporate finance. Two are managed in London and two are managed in Frankfurt.