The handful of quantitative trading firms that dominate market making in exchange-traded funds in Europe could be in for a bonanza if imminent rule changes send volumes soaring.

These firms – mostly privately owned, thinly staffed and users of highly quantitative and computational methods to trade – may see their bumper profits swell further in a market that could be blown wide open by the revised markets in financial instruments directive, or Mifid II, which comes into force at the start of 2018.