London has long battled with New York to become the world's financial capital but that bragging right is under threat as a possible "Brexit" looms.
Deutsche Bank is the first giant lender to review its operations in the UK as the country is set to have a vote on its membership of the EU by the end of 2017.
The German firm, which employs more than 8,000 workers in the UK, has reportedly set up a working group to investigate the fall-out from a possible UK exit from the 28-member bloc.
The group will consider whether moving some of the firm's operations into the eurozone would be beneficial in the event of a "Brexit", according to the Financial Times.
The move comes after the Tories secured a shock majority in the House of Commons at the general election. David Cameron had promised in the run-up to the vote that a Conservative government would hold an in/out referendum.
HSBC revealed earlier in the year that the bank is investigating whether to move its headquarters out of London if the electorate voted to leave the EU.
Douglas Flint, the firm's chairman, said in April: "As part of the broader strategic review taking place, the board has therefore now asked management to commence work to look at where the best place is for HSBC to be headquartered in this new environment.
"The question is a complex one, and it is too soon to say how long this will take or what the conclusion will be; but the work is under way."
But the business community seems divided over the historic vote as JCB boss Lord Bamford backed calls to leave the EU yesterday.
The chairman of the manufacturing firm told the BBC: "We are the fifth or sixth largest economy in the world. We could exist on our own -- peacefully and sensibly."
Elsewhere, the Institute of Directors (IoD) said a majority (60%) of its members wanted to stay within the EU on the condition that Brussels made concessions on key areas like employment law and corporate governance.
The survey, of more than 1,400 directors, found that only 31% of IoD members would vote to remain a member of the EU in all circumstances.
Deutsche Bank had not responded to a request from IBTimes UK for comment at the time of publication.