John Major wants to impose an energy tax on the Big 6 energy suppliers, and I have a lot of sympathy with his demand. But, and it's a very big but, I very much doubt that anyone can at present.

Of course legislation would be required, and could be passed, but what that legislation would also have to demand, because it is not available at present, is data from all six companies on just what they do in the UK.

None of the companies give clear data on their UK activities. I know this because of the work I did on Npower earlier this year for 38 Degrees. I also know it because I have checked the other companies. Four are not UK owned. Only one has a majority UK based trade. In no case is it clear just what profits are made in the UK alone and not elsewhere. There is, straightforwardly, massive opacity in this market.

There is, of course, an answer to that. What is needed is country-by-country reporting in this sector. If anyone is serious about regulating this market - as Ofgem should be - then they should not demand some limited accounting data from them, but full country-by-country reporting accounts. And this means full in the sense of country-by-country reporting accounts for the entire group of which the company is a member. It would be pointless demanding such information for the UK alone as that would not reveal the full financial flows in and out of the UK as well.

Only then will we know what these companies might make here, how that compares with other countries, and whether or not there is real reason for concern. Right now we're just whistling in the dark.

The solution is simple. Who will have the courage to ask for it?