Nomura, the Japanese financial group that acquired most of Lehman Brothers’ European operations last year, is embroiled in a bitter lawsuit with an ex-Lehman banker who claims he was forced out after raising concerns about conflicts of interest.

Paul Ryb, who worked in London as a telecommunications specialist, is taking Nomura to an employment tribunal for allegedly making him redundant after he complained Lehman executives deliberately misled clients to generate investment banking revenue.