New York Attorney-General Eliot Spitzer has widened his investigation into broker commissions, with four insurers receiving subpoenas to supply information. Chubb, Hartford, Aetna and Cigna have all announced they have been ordered to provide details of the commercial arrangements they have with leading brokers Marsh, Aon and Willis.

Mr Spitzer, who has carved a fearsome reputation for himself after successfully prosecuting stockbrokers for dubious practices involving analytical reports to clients, believes the brokers may have conflicts of interest because they receive commissions from insurers as well as fees from clients.

Reports from the US suggest that the investigation has put brokers under unprecedented scrutiny, with risk managers now demanding to know what arrangements their brokers have with insurers.

A public advocacy group, the Washington Legal Foundation, says the fees might compromise brokers’ fiduciary duties to their clients. Similar investigations are now also being conducted in Connecticut and California.

Spokesmen for the insurers said their companies will co-operate fully with the inquiry.