Rachel Reeves, Chancellor of the Exchequer, during a visit to University College London Hospital on Wednesday.

Britain’s Chancellor of the Exchequer Rachel Reeves announced nearly $50-billion worth of tax increases on Wednesday in a long-awaited budget speech that was upended by an embarrassing leak of every budget measure.

The leak came from the Office of Budget Responsibility, or OBR, an independent government agency that serves as a watchdog on public spending.

The OBR accidentally uploaded a detailed analysis of the budget on its website Wednesday morning, several hours before Ms. Reeves was set to unveil it in the House of Commons. The agency quickly removed the link but not before the report had been widely circulated.

“We apologize for this technical error and have initiated an

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