Fascinating stuff has just been released to my colleagues at the World Service, revealing the Treasury's assessments of what the war in Iraq might cost.
Documents prepared for Gordon Brown in the run-up to the 2003 Budget - and obtained by the BBC through freedom of information - say that the "best estimate" of the combat cost of the war is £3.1bn.
But that same document goes on to state clearly that the total "potential military costs" might be much more, some £5bn, since "the emerging politics of post-conflict Iraq are already pointing to a much more substantial commitment both in terms of size and length of stay".
But in the Budget a month after this document was drafted, there is no mention of the larger figure. Now, you would imagine that civil servants would prepare for a range of outcomes.
But at the very least this is an intriguing glimpse of the behind-the-scenes preparations for the Iraq war.