The group is hiring Mark Preston, a banking industry specialist, who quit Lloyds Bank before its ill-fated merger with HBoS.
Preston will work alongside City Index chief executive Martin Belsham, who has been at the group in a second stint for around four years.
There had been suggestions that Belsham was leaving too, although this was firmly denied yesterday. One rival questioned how happy he might be with the bringing in of an executive chairman who might question his authority.
Preston’s appointment follows the recent departure of the group’s chief operating officer Simon Bird.
Prior to his appointment at City Index, Bird had been at Bear Stearns from 1999 to 2008, having joined from NatWest Securities where he had been an equities and derivatives trader.
Spencer has been required to invest significantly in the firm in the recent past as it struggled to maintain margins in a highly competitive domestic market.