The EU's top banking regulator warned banks "to speed up their preparations for the potential departure of the UK from the EU in March 2019" without an agreement in place.
"Firms cannot take for granted that they continue to operate as at present nor can they rely on as yet unrealised political agreements or public policy interventions," Andrea Enria, Chairperson of the EBA, said.
He added: "Risks, capacity and legal implications must be examined and addressed."
International banks with their European headquarters based in London and British banks have been submitting applications to move some of their operations to the continent. And European banks that wish to continue trading and serving clients in London need permission to do so.
The EBA's intervention may be seen as an attempt to attract jobs and banks to the continent, as Dublin, Paris and Frankfurt step up their campaigns to become the financial capital of Europe.