An investment group that is majority-owned by Michael Spencer, founder and chief executive of ICAP, the interdealer broker, used shares in Numis as loan collateral without notifying the company, the stockbroker said on Tuesday.

Mr Spencer, who is also chairman of Numis as well as treasurer of the Conservative party, owns 55 per cent of IGPL, an investment vehicle which owns 13m ordinary Numis shares or 12 per cent of the share capital in the stockbroker, with his wife and family. IGPL also owns spread-betting company City Index.