A micro-tax on financial transactions. Basically, a way of skimming a sliver off all the action in your capital markets. Socialist governments love it because it really sticks it to the military financial industrial complex, financiers —especially high-frequency traders — hate it for pretty much the same reason, and point self-righteously the drag and compliance cost it puts on a market everyone wants to be as slick and efficient as possible, and how it pushes transactions away from domestic markets to shadowy offshore havens. You know the jazz. Anyway the French and the Italians have imposed one. Other European nations “haven't quite got round to it yet”., though what is SDRT?
See also