Office for Budget Responsibility chairman Robert Chote rebuked David Cameron today for misrepresenting its position on the affect of the government's cuts.
The head of the independent fiscal watchdog wrote to the Prime Minister to dispute claims made in a high-profile speech on Thursday.
Mr Cameron said the OBR was "absolutely clear that the deficit reduction plan is not responsible" for depressed growth - "in fact, quite the opposite."
But in a letter sent to Number 10 Mr Chote insisted that it in fact believed there was a short-term effect and that "fiscal consolidation measures have reduced economic growth over the past couple of years."
A Downing Street spokesman said: "The OBR has again highlighted external inflation shocks, the eurozone and financial sector difficulties as the reasons why their forecasts have come in lower than expected.
"That is precisely the point the Prime Minister was underlining."