Moody's expects the U.K.'s to leave the EU to pose newchallenges to non-British global investment banks' pan-European business modelsas the companies could lose the passporting rights that allow them to offerproducts and services across the U.K. and the EU.

Michael Eberhardt, a senior credit officer at Moody's, saidsuch firms may incur additional costs and revenue pressures amid efforts toreconfigure their European businesses in response to Brexit.

"This comes at a time when European investment banksare facing pressures from subdued market activity, regulation and competitivepressure that have depressed investment banking and trading revenues,"Eberhardt noted.

The agency added that the two-year timeframe to negotiatewithdrawal from the EU places considerable pressure on the companies to adaptorganizational structures, reposition their U.K. and EU businesses and addressmost operational and personnel issues.

Moody's, however, noted that the added operations challengesand costs will be manageable in the context of the companies' global earningsand operations. The agency said a mitigating factor was that many firms arealready licensed to operate from multiple jurisdictions within the bloc.

"In addition, the global scope of these firms'franchises limits the potential impact of Brexit on their overall revenue andincome," the agency said.