Let me add very briefly that from an economic perspective you might want to introduce that type of thing to seek to incentivize people to use less and make more efficient use of energy.
What we have to recognize, though, and perhaps this is where having a comprehensive anti-poverty strategy comes in, is that if we going to do this, we have to be prepared to find other ways of compensating those on low incomes for this system, which might make very good sense from the point of view of society as a whole. People are suffering, as you will know, substantial real impacts on their real incomes as a result of fuel and food increases at the moment. In some sense, the tax is just another issue on the top of that.
I think one has to perhaps look again at certain questions, which David Gordon has spoken about—the value of benefits and so forth, but also perhaps the value of income taxes to people at the bottom—to see whether there are ways. If one's going to be radical in that fashion with carbon taxes, I think you have to do these other things as well to make sure that those at the bottom do not suffer in any sense disproportionately.