The agreed takeover of Sedgwick plc by the giant US insurance brokerage, Marsh & McLennan, is set to widen the gap between the number one and number two world ranked players by around $2 billion, according to those who calculate such figures. But the number two international player - the Aon Corp - obviously has disigns on bigger things if its name is anything to judge by. The corporation's boss, Chicago-born Pat Ryan, has a lot of regard for the auld sod and Aon is of course an Irish word - as in uimhir a h-aon.