(Reuters) - Citigroup Inc
Jim Cowles, Citi chief executive officer for Europe, Middle East and Africa, told the Financial Times that there was "mounting concern" among clients about their ability to use the United Kingdom as a regional hub if the country exits the EU.
"It is not that international companies will stop investing in Britain, but their investment just will not be at the scale we have become accustomed to," Cowles told the newspaper.
He added that the existing trade arrangements will be at risk and Britain will have no influence in making the rules in the future.
Citigroup is the latest corporation to say it favors Britain continuing its membership of the 28-member trading bloc after Prime Minister David Cameron promised voters he would renegotiate the terms of Britain's EU membership before holding an in-out referendum by 2017 if his ruling Conservatives were returned to power after elections due in May 2015.
According to the Financial Times, the British Bankers' Association has also sent a submission to a Treasury review of powers between the United Kingdom and Germany. The submission said that a single market for financial services is a significant factor in the success of the United Kingdom as a financial center, and of considerable value to the UK economy.
European aerospace group Airbus
The London-based Centre for European Reform (CER) predicted last week that Britain would struggle to maintain trade with other EU member states - now 54 percent of goods trade - if it left the bloc.
British finance minister George Osborne recently warned the European Union that it must reform if it wants Britain to remain a member, and said it faces decline if it resists change.
(Reporting by Aashika Jain in Bangalore; Editing by Lisa Shumaker)