Marsh & McLennan may have to pay over £20m to its arch-rival Aon Corporation next week, after Aon scooped up shares worth £18m in Sedgwick.
Aon stands to profit by £2.4m if the bid for Sedgwick goes through as expected on 20 October.
The shares were bought by subsidiary Aon Advisors UK at around 197p and gives Aon 1.6 per cent of the company. The Marsh & McLennan offer price is 225p per share.
If the deal fails, and it is still awaiting regulatory approval from the US Federal Trade Commission, it places Aon in a good position to make a rival bid.