Citigroup is moving to secure its future in the competitive world of share trading. It will roll out a new high-speed electronic system that aims to sniff out the best price available for shares its clients want to buy or sell on any of several competing exchanges operating once new European rules take effect from Thursday.

The Markets in Financial Instruments Directive (Mifid) allows many venues to compete with local stock exchanges, a development that poses challenges for brokers. Share trading takes place in milliseconds, and a broker will have to seek out the best price on more than one system.