Mind the output gap, or the politics of facts

Here's an excellent piece of rapid debunking of Treasury rhetoric by Robert Chote, Director of the Institute for Fiscal Studies. The basic point he makes is important. The Treasury would like to write recent economic history to be as consistent as possible with the "end of boom and bust" Brown used to boast of. The official account from the budget is that "the productive potential of the economy grew by almost 3½% a year inLabour's first term and then by roughly 2¾% a year thereafter until thecrisis hit and trend growth fell to 1% a year for three years". Odd to make "trend" growth fall for just three years, isn't it?As Chote says, the alternative (and more plausible) view is that trend growth has been pretty constant at 2.6% since 1997, but that worldwide falling prices (from ex-USSR raw materials and Chinese workers) blinded policy-makers to the fact that they were running highly inflationary policy throughout the period when growth was higher than trend. So the end of "Tory boom and bust" in fact meant the arrival of Gordon's alternative: "HUGE boom, followed by HUGE bust". Over and above the intrinsic interest of the analysis, there is an important point here about the political manipulation of history. Why are public servants involved in massaging facts for political reputations? Can we have a real Parliament with the equivalent of the US's Congressional Budget Office  since we can no longer trust the Treasury to give us plain data?