Chancellor George Osborne has been strongly criticised by MPs for using his annual Autumn Statement on the economy as a second full-scale Budget.
The cross-party Commons Treasury Committee said that having two major scale fiscal statements each year added to the "potential uncertainty" for business and the wider economy.
In his last Autumn Statement in December, Mr Osborne announced a series of changes - including a £3.7 billion benefits squeeze and a rise in tax thresholds - as well as admitting he would miss a key target for reducing the deficit.
He was urged by the committee to re-establish the spring Budget as the focus of fiscal policymaking, with the Autumn Statement no more than an "updating" of the position.
"There are good reasons for having a single substantial annual review of the fiscal and economic state of the country," it said.
The way the Chancellor used the Autumn Statement to scrap a planned increase in fuel duty had, the committee said, failed to provide "either the certainty or the stability that are the hallmarks of good tax policy".
The committee chairman, Tory MP Andrew Tyrie, said: "The Autumn Statement is not, nor should it be, a second Budget. In recent years it has come to read like one.
"The case for two Budgets is weak. An additional one can create uncertainty and carries an economic cost. Only in an emergency would it be likely to carry long-term benefit.
"The primacy of the Budget as the main focus of fiscal and economic policy making should be re-established."
The committee expressed concern that the economic forecasts of the independent Office for Budget Responsibility (OBR) - established by Mr Osborne to take over forecasting from the Treasury - had been "biased to over-optimism".