Rachel Reeves's Budget was accessed almost 25,000 times before its official publication following the Office for Budget Responsibility (OBR) leak. A report by the National Cyber Security Centre (NCSC) showed there were at least 24,701 downloads of the official OBR forecasts in the hour before the Chancellor delivered her Budget on November 26. This was much higher than the 43 occasions reported in an initial review.

According to the report, the first full download of the OBR's forecasts happened just after 11.35am on the morning of the Budget, after more than 500 unsuccessful attempts.

With the report spreading on social media, Britain's cyber security unit said the file was then downloaded tens of thousands of times. The investigation also found that Ms Reeves's Spring Statement last March was accessed 16 times before her speech, not once as previously thought.

The damaging leak led to Richard Hughes' resignation as OBR chairman, which the organisation described as the worst failure in its 15-year history.

Kenny MacAulay, CEO of accounting software platform Acting Office said: "It beggars belief that market sensitive data can fall into the hands of tens of thousands of people due to sloppy document management in advance of such an important speech.

"Basic compliance requitements should be in place to prevent data leakage like this from happening, with the process around uploading of major reports thoroughly reviewed so confidential information remains under lock and key until the correct time."

Security expert Graeme Stewart, head of public sector at Check Point said: "The calamitous security breach underlines the very real risks associated with the leakage of sensitive economic data. With tens of thousands of people able to access the entire economic forecast in advance of the Chancellor's speech, the opportunity for hackers and fraudsters to play the markets is immense.

"There are no credible excuses for such incidents to occur, and the government needs to initiate a complete rethink of its publication strategy."

Mr Hughes's resignation also followed weeks of tensions between the Treasury and the fiscal watchdog after the OBR's decision to downgrade its assessment of long term UK growth. Ms Reeves was later accused of misleading people over the state of the public finances after government briefings suggested the outlook for the economy was worse than later revealed, The Telegraph reported.

The Treasury said it was taking several steps to improve the security and integrity of forecasts going forward. Future OBR documents will now be published on the Government's official website.

The Treasury said: "The OBR will consider, ahead of Budget 2026, whether the current approach to publishing the timetable continues to contribute to transparency and stability as was intended when it was implemented in October 2022."

The Daily Express has contacted the Treasury for a comment.