A major leak of the Office for Budget Responsibility’s (OBR) economic and fiscal outlook has exposed key projections ahead of the chancellor’s Budget, triggering calls for an inquiry and raising political tensions.

According to figures, shared by Reuters from the leaked documents, the OBR now expects real GDP to grow by an average of 1.5% over the forecast period.

This is 0.3 percentage points lower than its March projection, attributed to weaker underlying productivity growth.

The leak, believed to have occurred after the full forecast was mistakenly uploaded to the OBR’s website, has overshadowed the final countdown to the Budget.

Liberal Democrat leader Ed Davey claimed the leaked OBR forecasts show taxes are set to reach a record high, accusing the government of presiding over a worsening squeeze on households and businesses.

Labour leader Keir Starmer acknowledged the seriousness of the leak but stopped short of calling for an investigation, saying the Budget was imminent. However, the scale of the disclosure, given the sensitivity of the OBR projections, is likely to prompt calls for a formal inquiry.

Conservative leader Kemi Badenoch asked whether Labour would support an inquiry into how the OBR’s full economic and fiscal outlook appeared online ahead of its planned publication.