I dislike focusing on this policy, though I do agree with it, as it's the rich who need to be paying more tax, not simply non-UK citizens who benefit from this law (which admittedly, if implemented, would simply make them pay the same as the equivalent UK national)
Having said that, I don't know what the right policy to tax the super rich more is - on a global scale, as has been said, these people are very mobile - but it is amongst the most important things that we need to be doing. You only need to look at the flow of wealth from the rest of society to it's upper eschalons over the last 20 years or so (which has been noted in numerous studies) and ask yourself "Well, did they earn it?" Or even better "Do they need it?". Simply accepting that this is how it has to be is to do ourselves a disservice, and really just puts us in quite a servile position. These people aren't gods - they should not be allowed to place themselves in such a lordship over the rest of humanity, which they clearly feel either contempt or else indifference for, given that many of them simply move to where they pay the minimum amount into the public purse.
Or do they - we won't know completely until we start trying policies such as these.