The U.K.’s budget watchdog has taken full responsibility for the unprecedented early publication of its budget forecast — but warned that it may happen again if its arrangements don’t change.

Last week, the Office for Budget Responsibility’s economic and fiscal outlook — which contained detailed information on what would be in the budget — was accidentally made accessible before Chancellor Rachel Reeves delivered her budget in parliament. 

In its investigation into what happened, the OBR said the “pressure on the small team involved” to ensure that the fiscal forecast was published immediately after Reeves finished her speech on Nov. 26 led to the use of a “pre-publication facility” which although is “commonly used” creates a “potential vulnerability if not configured properly.”

“The twice-yearly task of publishing a large and sensitive document is out of scale with virtually all of the rest of its publication activities,” said the investigation, which was hastily carried out by peer Sarah Hogg and OBR board member and City bigwig Susan Rice.

It called for “completely new arrangements” to be put in place for the publication of market-sensitive documents, and urged the Treasury to pay “greater attention” to the need for adequate support when funding the OBR.

The watchdog said that given its small size, it used an outside web developer to upload its contents. It found multiple attempts by outside parties to access the document before it was published, by guessing the URL, and also revealed there was a successful attempt to do so in an earlier major March publication.

On Nov. 26, the day of the budget, there were 44 unsuccessful requests to the URL between 5.16 and 11.30 a.m. as the document had not yet been uploaded.

Between 11.30 and 11.35 a.m., the web developer began uploading documents to the draft area of the OBR’s website, which the watchdog believed was not publicly accessible. At 11.35 a.m., an IP address which had made 32 previous unsuccessful attempts to gain access to the site accessed it for the first time successfully.

Six minutes later, at 11.41 a.m., Reuters sent a news alert reporting the government would raise taxes by £26.1 billion by 2029-2030. The URL was then widely accessed by journalists, markets and other parties between 11.30 a.m. and 12.08 p.m., after which it was removed by the OBR.

The report also reveals that one IP address successfully accessed the March version of the fiscal outlook, when Reeves delivered her spring statement. The log shows the document being accessed at 12.38 p.m., five minutes after Reeves started speaking and nearly 30 minutes before publication.

“It is not known what, if any, action was taken as a result of this access and there is no evidence at this stage of any nefarious activity arising from it,” the report says.

The report doesn’t review how financial markets were influenced by the early publication, but says the OBR will cooperate with the Financial Conduct Authority.

The investigation described the mistake as the “worst failure” in the 15-year history of the OBR, but said that it was not a case of intentional leakage, or “pressing the publication key too early.” 

OBR chief Richard Hughes is due to appear before MPs Dec. 2 where he will be fighting for his future. Speaking to Sky News on Sunday, the chancellor repeatedly declined to say whether Hughes was safe in his job. 

Earlier today, Keir Starmer said that while he was “very supportive” of the OBR, the breach of market-sensitive information was a “massive discourtesy” to parliament.