I have always hated politicians (present company excepted) who spoke about Tobin taxes because they rarely properly understood the idea. I hate it even more now its called a Robin Hood Tax because its making something that is quite difficult to understand even more unintelligible. The principle aim of these kinds of taxes is to increase the cost for short term investors – in effect rigging the market in favour of long term investors. It is not a cash raising measure per se but a behaviour modifier – or “nudge” if you prefer. It was initially suggested in the context of currency trades to stop the daily dash from one currency to another in search of quick gains that had adverse impacts on the “victim” states – although now, ppl think the idea might be applicable to any transaction where speculators may operate. My principle issue with the robin hood tax is that – if the policy is successful and the rate of the tax set appropriately then the revenue raised under it should be low to insignificant – so why should we promise an insignificant or low amount of money to important good causes? I’m yet to hear a satisfactory answer to this question.