The Office for National Statistics (ONS) said gross domestic product contracted by 0.1 per cent in the August-to-October period.
Economists polled by Reuters had forecast a flat reading.
In October alone, the economy contracted by 0.1 per cent, against forecasts for a 0.1 per cent rise.
While single-month GDP figures are volatile and prone to revision, Friday's data means the economy has not grown since June.
That underlined the tough economic backdrop that finance minister Rachel Reeves faced when she readied a big tax-raising budget that she announced on November 26.
Sterling fell slightly against the US dollar on the back of the data, which showed unexpectedly sharp declines in the dominant services sector as well as construction.
Friday's data also casts doubt on the BoE's expectation that the economy will grow about 0.3 per cent in the fourth quarter as a whole.
On Thursday, investors assigned a roughly 90 per cent chance of a BoE interest rate cut on December 18.
Manufacturing output, impaired in September by a cyber attack on Jaguar Land Rover, failed to recover as economists had hoped.
The ONS said retailers in particular had a bad month, part of the reason why services output contracted by 0.3 per cent in October against forecasts for a flat reading.
In response to the data, the finance ministry said it was determined to defy the forecasts on growth and create good jobs.
Compared with a year earlier, economic output was 1.1 per cent higher in October, the ONS said, weaker than the 1.4 per cent expansion forecast by economists.
