NEW YORK (TheStreet) -- Barclays  (BCS) - Get Report  stock is plunging 23.28% to $6.82 on heavy trading volume late Monday morning as shares of British banks continue to tumble after the U.K. unexpectedly decided to exit the European Union early Friday. 

Barclays CEO Jes Staley faces the toughest challenge among leaders of British banks because he is committed to running a large, London-based investment bank, Jefferies analysts wrote in a note cited by Bloomberg. 

Friday's decision "changes everything about Barclays's investment proposition," Jefferies contended. The "structure, profitability and, indeed, existence of Barclays's investment bank are called into question," and "the U.K. referendum is likely to require an expensive reshape of the investment bank."

Following the vote, London's banks might lose the banking passport system that allows them to operate throughout the region without setting up local subsidiaries, Bloomberg reports. If Britain loses this right, Barclays would have to undertake the costly task of bolstering operations in cities such as Frankfurt and Dublin.

Additionally, Barclays's revenue will drop as British bond and loan issuance decline. 

About 75.63 million shares of Barclays have been traded so far today, well above its average trading volume of roughly 7.22 million shares per day. 

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