The chair of the Office for Budget Responsibility has said he felt mortified by the early release of its budget forecasts as the watchdog launched a rapid inquiry into how it had “inadvertently made it possible” to see the documents.

Richard Hughes said he had written to the chancellor, Rachel Reeves , and the chair of the Treasury select committee, Meg Hillier, to apologise.

“I felt personally mortified by what happened. The OBR prides itself on our professionalism. We let people down yesterday and we’ll make sure it doesn’t happen again,” he told BBC Radio 4’s Today programme.

Reuters, the agency that first published excerpts of the outlook on its news wire, revealed on Thursday how it had obtained the document.

It said: “The document, which is usually published after the finance

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