The Robin Hood Tax (aka Stamp Duty)
Using the name "Robin Hood Tax" is misleading because it implies that it is a new tax.
The UK has had a Financial Transaction Tax for many years. It is called Stamp Duty. The logic is quite simple. For transactions in shares to have any merit then there has to be a legal system. People should pay on an ad valorem basis for this.
This happens in England and in Ireland. England charges 0.5% and Ireland 1%.
My view is a simple one which is that the tax havens piggyback on top of the global systems which are substantially maintained by the higher tax countries. It is, therefore, quite reasonable that such a transactional tax should be paid more widely.
Hence I am supporting the extension of this to a global system. I have, however, been quite clear that it cannot be done unilaterally. This would simply move trading around to locations without the transaction tax and actually would be likely to reduce the UK's Stamp Duty revenue.
The Tobin tax is a proposal to also tax currency exchanges. It is a relatively low value tax. The argument is more finely balanced for countries with smaller currencies as they would tend to lose out. However, it could be a good mechanism for raising some funds. It would, however, reduce the number of transactions and hence the funds raised would not be as great as has been thought.