Britain's gross domestic product shrank in the July-to-September period and was flat in the previous three months, according to updated official figures that suggested the economy might now be in a recession.
GDP contracted by 0.1% in the third quarter, the Office for National Statistics said on Friday.
It had previously estimated that the economy showed no change compared with the previous three months and economists polled by Reuters had mostly expected another unchanged reading.
The ONS also said economic output in the second quarter was now estimated to have shown no growth, a downwards revision from a previous estimate of 0.2% growth.
However, separate data showed retail sales in November jumped by much more than expected, increasing by 1.3% from October.
Sterling rose against the dollar and the euro after the data releases.
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Finance minister Jeremy Hunt, whose Conservative Party is lagging in opinion polls ahead of an expected election next year, said the outlook for the economy was not as bad as the updated official figures suggested.
The medium-term outlook for the UK economy is far more optimistic than these numbers suggest," Hunt said in a statement.