Tom King, chief executive of Barclays investment bank, also said at the Barclays Financial Services Conference there were tentative signs of a pick-up in trading activity after a slow July and august.

"We are in a cyclically slower part of the year. For this quarter it's usually about September. It's very early days, but September seems to have the hallmarks of what could be a nice, attractive month, we're seeing a bit of volatility in the trading business and the issuance calendar is robust," King said.

(Reporting by Steve Slater; Editing by Anjuli Davies)