A former Citigroup analyst who quit the industry in April has topped a closely-watched ranking of investment banks' researchers in Europe, highlighting the challenges banks face keeping hold of top talent as investors have cut back their research spend in the wake of sweeping regulation.

Mark Manduca, who worked at Citigroup covering the transport sector, left the bank in April to join XPO Logistics as its chief investment officer. He was voted the best analyst in developed Europe for the second year running by fund managers in the Institutional Investor rankings, known in the industry as the 'City Oscars'.