It was not so long ago that gaining access to high-frequency trading firms seemed almost as difficult as getting an audience with the Pope. How times have changed. As quickly as the firms became major participants across western stock exchanges, they have added a distinctly public face.

The firms' leaders - many of whom are now loquacious ex-bankers rather than camera-shy technologists - have become regular speakers at industry conferences. Meanwhile, a group of over 20 of Europe's largest HFTs have joined forces over the past year through an industry trade association, giving the firms a powerful voice in front of regulators.