Who to believe?
Does anyone believe the government's own spending assumptions? I ask because this week both the prime minister and the first secretary of state (aka Lord Mandelson) have seemed to suggest that they were a bit iffy.
Okay, so they didn't exactly put it that way. But that was the implication.
Consider, first, the prime minister, in today's knockabout with the leader of the opposition. In round three (or is it 42?) of the Spending Cuts Saga, he once again insisted that current spending would rise after 2011 under Labour, but be cut by the Conservatives.
I won't go back over the main elements of the spending row right now (I have written a quick primer on the numbers below, for those that want it). But for me, one of the big unanswered questions in this debate has been whether or not the government actually disputes the IFS numbers which are so often quoted against them.
All that the Treasury says is that "they are not our numbers". But, at times, both the prime minister and Ed Balls have appeared to suggest that there will be more space for spending growth than the IFS implies, because unemployment and other "unavoidable" costs will be lower than they think.
The PM was gesturing in this direction today when he said that Mr Cameron's spending plans were based on a rise in unemployment "because you will do absolutely nothing about it".
But, you'll recall that the Conservative figures are taken from the IFS, which are themselves based largely on the Budget's own unemployment forecasts, or the Department for Work and Pension's long-term forecasts for benefit spending.
So any problem the prime minister has with the Conservative/IFS numbers would surely apply to the government's numbers as well. I wonder if the prime minister knows something the chancellor doesn't.
I had the same thought listening to Lord Mandelson's comments on the Today programme on Monday, when he said that it wouldn't be right to make spending plans based on "speculative projections".
The first secretary of state said "we are not in a position to be able to forecast what growth will be or the performance of the economy will be in 2011-12". Evan Davis pointed out that the Budget had indeed made just such a forecast - in fact, based the government's spending and tax plans on it.
Mandelson replied that any such forecasts were "entirely speculative," and it would be better to base spending on "reality, not speculation".
So, neither the prime minister nor Lord Mandelson seem to put much store by what the Treasury says these days. Curious times indeed.
PS. A PRIMER ON THE SPENDING DEBATE
There have been some interesting twists and turns along the way, but these are the basic facts which have kept the barbs flying over the dispatch box for so many weeks.
The numbers in the Budget suggest that total spending between 2011 and 2014 will fall in real terms by 0.1% a year. In other words, essentially flat.
But that total includes a massive (and now much-discussed) cut in capital spending of 17.3% a year over that period. The prime minister suggested recently that asset sales would make up the difference, but the government has not identified things to sell that would come close to filling the gap.
That leaves current spending - everything that isn't capital investment. That is due to grow in real terms by 0.7% a year, the lowest growth since 1997-2000 when Labour was following through on the previous government's spending plans.
So, current spending will grow from 2011 to 2014, as the prime minister suggested today. But, as has been thrashed out many times over the past few weeks, that figure includes the rising cost of social security and debt interest. If you take those and other "uncontrollables" into account, the IFS says that current spending on everything else will fall in real terms by 2.3% a year.
If you protect health and development spending from real terms cuts, as the shadow chancellor promised once again yesterday in his interview with Nick Robinson, other current spending would have to fall by 3.3% a year in real terms - or roughly 10% over three years. If schools are also protected, as Ed Balls has sometimes suggested, there would need to be cuts in other spending of 13.5% over three years.