The Telegraph reports:

In a letter to the Shadow Chancellor, George Osborne, the permanent secretary to the Treasury, Nicholas Macpherson, acknowledged that the figures used by the Chancellor to undermine Tory plans to impose a tax on foreign workers in the UK should only be treated with "a great deal of caution".

He admitted:

there is no complete data set for the unremitted foreign income of non-domiciles.

And added:

All figures are best estimates but need to be treated with a great deal of caution due to the lack of available data or evidence.

I can see why the Tories are miffed. I also feel justified in dismissing Labour's claim.

And in calling for the Treasury to get on and publish what they really know.

And come to that, for saying I've still calculated the only reliable figure we've got.