FILE PHOTO - The corporate logo of financial firm Morgan Stanley is pictured on the company's world headquarters in New York, New York, U.S. on January 20, 2015. REUTERS/Mike Segar/File Photo

LONDON (Reuters) - U.S. bank Morgan Stanley MS.N may initially move 300 staff from Britain following its exit from the European Union, and is scouting for office space in Frankfurt and Dublin, Bloomberg News reported on Thursday.

The Wall Street firm will eventually choose either Frankfurt or Dublin to base its enlarged European Union hub, according to the Bloomberg report, which cited three people with knowledge of the matter.

Leading financial firms warned for months before last June’s Brexit referendum that they would have to move some jobs if there was a leave vote, and have been working on plans for how they would do so for the past several months.

More details are starting to emerge after Prime Minister Theresa May confirmed Britain would leave the European single market, ending banks’ hopes they might retain “passporting” rights that let them sell their services across the EU out of their London hubs.

Morgan Stanley, which bases the bulk of its European staff in Britain, will have to move up to 1,000 jobs in sales and trading, risk management, legal and compliance, as well as slimming the back office in favor of locations overseas, a source involved in the process told Reuters in January.

“Our focus is on ensuring that we can continue to service our clients whatever the Brexit outcome,” Hugh Fraser, a spokesman for Morgan Stanley in London, said in response to the report.

“Our strong franchise and material presence in Europe gives us many options, and we will adapt as the details of Brexit become clear. Given all of this, no decisions have yet been made.”