Increase to £17.8bn is well above City forecasts and is highest December figure for four years

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UK government borrowing jumped unexpectedly to £17.8bn last month, piling pressure on Rachel Reeves to plan budget cuts before a spending review in the summer.

The figure was about a quarter higher than the City had forecast and was up by £10.1bn more than in the same month a year earlier, making it the highest December borrowing for four years.