LONDON — A vast swathe of Britain’s government-wide budget leaked almost an hour ahead of time Wednesday, in an apparent Whitehall blunder that’s already got the opposition Conservatives demanding an inquiry. 

Scrutiny documents posted on the website of Britain’s fiscal watchdog the Office for Budget Responsibility (OBR) — normally made public once Chancellor Rachel Reeves sits down following a House of Commons speech — lay bare the impact of Reeves’ latest tax-and-spend statement on the British economy, and detail a raft of the policy measures she will take. 

The documents have since been removed, but the OBR makes clear that Reeves will unveil £26 billion-worth of tax rises — and that the U.K.’s tax take will hit a record 38 percent as a proportion of GDP by 2031. 

The British economy is forecast to grow by just 1.5 percent over the OBR’s current forecast period, 0.3 percent slower than projected in March, with the watchdog blaming poor productivity growth.

Speaking in the House of Commons just before the budget announcement kicked off, Tory Leader Kemi Badenoch condemned the “unprecedented leak” and demanded an investigation to “punish those responsible.”

Prime Minister Keir Starmer rejected the need for a leak inquiry, stressing it was “literally about 25 minutes before the budget will be set out in full, where we’ll take further decisions. The chancellor will set it out.”

The Office for Budget Responsibility said Wednesday: “A link to our Economic and fiscal outlook document went live on our website too early this morning. It has been removed.

“We apologise for this technical error and have initiated an investigation into how this happened.

“We will be reporting to our Oversight Board, the Treasury, and the Commons Treasury Committee on how this happened, and we will make sure this does not happen again.

“Our Economic and fiscal outlook and supporting documents will be released when the Chancellor has finished her speech.”

This developing story is being updated.