MPs have opened a wide-ranging inquiry into the Office for Budget Responsibility, signalling a fresh round of parliamentary scrutiny for the UK’s fiscal watchdog after a turbulent autumn marked by leaks, disputed briefings and the resignation of its chair.

The Commons Treasury Committee said it would examine the OBR’s forecasting record, its independence and impartiality, and whether the way it works with the Treasury remains fit for purpose 15 years after the body was established. The cross-party committee, chaired by Labour’s Meg Hillier, has invited written evidence by 30 January.

The move comes as ministers and officials continue to deal with the fallout from Chancellor Rachel Reeves’s first full Budget, when the OBR’s Economic and Fiscal Outlook was made accessible online before Reeves delivered her statement to MPs. The OBR later described the early publication as the “worst failure in the 15-year history” of the organisation, and Richard Hughes, then chair of the watchdog, resigned after accepting “full responsibility” for procedural weaknesses that allowed the breach.

While the committee stressed the inquiry was intended to be constructive, it lands amid strained relations between the watchdog and the Treasury over the way forecasts were discussed in the run-up to the Budget and the political handling of sensitive fiscal information.

Announcing the inquiry, Hillier sought to frame it as an attempt to strengthen the institution rather than undermine it. “This inquiry is not a stick to beat the OBR with,” she said, adding that MPs wanted “an honest conversation about what the watchdog does well and where it needs to do better”.

The OBR was created in 2010 by the then chancellor George Osborne to provide independent economic and fiscal forecasts, replacing a system in which the Treasury produced the headline numbers underpinning Budgets. Its twice-yearly forecasts are central to the government’s fiscal framework, affecting judgments about borrowing, debt and the room available for tax and spending decisions.

That role acquired added political sensitivity after Liz Truss’s government triggered market turmoil in 2022 by pressing ahead with a “mini-budget” without an accompanying OBR forecast. Hillier referenced that episode in warning about the consequences of sidelining the watchdog, a point that has often been invoked across parties as a lesson in the importance of credibility with investors.

The current dispute has been less about whether the OBR should exist than about how it operates, how its work is communicated and whether its processes are robust enough to withstand modern pressures. In late November, Hughes sent an unusually detailed letter to the Treasury Committee setting out how the watchdog’s view of the public finances evolved in the run-up to Reeves’s Budget, pushing back on claims that the chancellor’s decisions were driven by a sudden, late improvement in the outlook. Reports at the time suggested the OBR’s pre-measures forecast on 31 October left Reeves with about £4.2bn of “headroom” against her main fiscal rule, before policy decisions were finalised.

The OBR has also complained publicly about pre-Budget reporting that it said spread “misconceptions” about its work. Giving evidence to MPs on 2 December, David Miles, a member of the OBR’s budget responsibility committee, said there had been a “flurry of leaks” before the Budget and that the watchdog had raised concerns with senior Treasury officials. He suggested the uncertainty created by repeated briefings could itself be economically harmful, while noting that the OBR could not easily intervene to correct misreporting during the sensitive pre-Budget period.

Reeves has condemned the leaks as “unacceptable” and “damaging” and told MPs she did not authorise any briefings. She has also confirmed that an internal Treasury investigation, overseen by the department’s permanent secretary, is examining who leaked Budget details.

Against that backdrop, the Treasury Committee said it would review not only the accuracy and presentation of OBR forecasts, but the boundary between close working and undue influence. Although the watchdog is legally independent, it relies on extensive information-sharing with government departments and works to tight Budget timetables set by the Treasury. Parliament also has leverage: the Treasury Committee effectively holds a veto over appointments to the OBR’s leadership.

The inquiry will give MPs a forum to weigh reforms that could range from changes to the watchdog’s remit and communications, to tighter security and publication controls, and possible revisions to the formal relationship between the OBR and the Treasury. For a government that has pledged to anchor policy in “rules-based” fiscal discipline, the handling of the watchdog that polices those rules now looks set to become a test of both competence and credibility.