Bank of England Governor Mervyn King criticised Chancellor Gordon Brown's decision to pin down exactly when an economic cycle starts and finishes.
Mr Brown last month changed the Treasury's estimate of the start of the current cycle to 1997 from 1999 based on revisions to past economic data - a move that gave him extra leeway to meet his selfimposed fiscal rules.
Mr King said monetary policymakers would rather not use such precise dates when looking at the ups and downs of the economy over time.
"The Bank and the Treasury have a very different view of how to think about the cycle. We don't like this sort of fixed dating and we have a different way of thinking about the economy and how it evolves," Mr King said.
"I am not even sure whether it makes sense to think about the cycle as a well defined phenomenon."
Mr Brown said in mid-July that new data suggested the economic cycle started in 1997. That allowed him some ten billion pounds extra margin of error on his "golden rule" --that the Government borrows only to invest over the cycle.
But analysts still say tax hikes will be necessary when the next economic cycle starts to fix a structural deficit.
Mr King said it was very difficult to determine for certain where the economy was headed, albeit when he too was in the midst of presenting downward revisions to the BoE's near-term outlook for growth but ramping up forecasts for further out.
"We don't even know where we are, we don't even know where the economy was a year ago. That will be revised. Indeed, the Chancellor does not even know where it was seven or eight years ago," Mr King said.