Goldman Sachs chief Lloyd Blankfein has warned the City will "stall" and could even "backtrack" as a result of Brexit.
Blankfein told the BBC his firm has made "contingency plans" to move people out of Britain depending on how negotiations play out with Brussels, and that he had been in discussions with European cities about moving.
However, he said Goldman Sachs doesn't have a comprehensive set of plans at the moment.
Speaking about the City, Blankfein said: "I don't think it will totally reverse... It will stall, it might backtrack a bit, it just depends on a lot of things about which we are uncertain and I know there isn't certainty at the moment."
Richard Gnodde, chief executive of Goldman Sachs' European arm, said the bank, which has around 6,000 staff in London, would start carrying out its contingency plans before the start of Brexit in 2019.