Mehmet Dalman, the investment banker who built Commerzbank Securities from scratch, has clashed with the bank's top management over what his London staff see as a policy of artificially depressing the reported profits they earn.

The dispute is certain to heighten speculation that Dalman may decide to leave Commerzbank, Germany's fourth-largest bank. Last week Dalman's operation posted a 36% rise in trading profit to €315m ($375m), a percentage increase that far outstripped the commercial bank.