The chairman and chief executive of asset manager BlackRock has said the firm’s role advising Ireland on a portfolio of toxic assets represents a bigger challenge than anything thrown up by the financial crisis in the US.

BlackRock Solutions, the division that aims to help the fund manager's institutional clients manage risk and which has developed its own models to value complex or illiquid securities, took on 20 new assignments in the fourth quarter and now manages $13.5 trillion.