The world's three biggest brokers – Aon Corporation, Marsh and Willis – are being sued by a California attorney for failing to disclose contingency fees.

It has prompted Association of Insurance and Risk Managers (Airmic) to reiterate its earlier calls for transparency of deals in the UK insurance industry.

The brokers are alleged to have made arrangements with insurers where they earn commissions based on the volumes of business placed.

David Gamble, executive director of Airmic, said: "We believe apart from helping to promote business confidence and trust, more openness has the potential to improve efficiency and effectiveness within the market."

He said Airmic had submitted a proposed code of conduct for Lloyd's brokers to the Treasury and was continuing dialogue with brokers and insurers.