MFS Investment Management, the $140bn (€114bn) US mutual fund firm, has unveiled a raft of new policies designed to regain the trust of investors after it was tainted by the improper trading scandal that has swept the US.

The proposals include a ban on all soft-dollar arrangements, in which fund companies pay brokerage firms an inflated trading commission. The brokerage firm pockets the trading costs, and then uses the premium to buy independent research or other services on behalf of the fund company.