Following a late start, Aon Hewitt’s fiduciary consulting business is growing at a rate that has stunned its rivals. It has pushed up its fiduciary clients from $18bn to $31.5bn in just over a year, after winning its first client only in 2010.

To an extent, Aon is taking the "easy" route of persuading its existing clients to convert to a fiduciary arrangement, which empowers consultants to match liabilities and select managers on their behalf. This client conversion helped Mercer boost its global fiduciary pool to $75bn following wins of $10bn last year. Towers Watson looks after nearly $60bn.