An unexpected slowdown in high-street spending for everything from household goods to food saw the worst fall in retail sales for five years last month, said official data.
Figures from the Office for National Statistics (ONS) said retail volumes dropped 1.9% month-on-month in December, far below economists' forecasts of a 0.4% decline and the biggest fall since April 2012.
But ONS senior statistician Kate Davies said consumers still spent strongly over the final quarter of the year as a whole.
She said: "Retailers saw a strong end to 2016 with sales in the final quarter up 5.6% on the same period last year, although the amount bought fell between November and December once the effects of Christmas are removed."
A reason for the December slowdown economists said may be that prices started to rise for the first time in 18 months in December.
Average store prices increased by 0.9% on the year last month, mainly due to the rise in petrol prices. Excluding fuel prices, shop goods edged up 0.1%, the first increase since June 2014.
Economists also pointed to consumers scaling back on purchases after taking advantage of Black Friday discounts in November.
Consumer spending has been robust since June's Brexit vote, but in recent months they now face a squeeze from rapidly accelerating inflation as the weak pound pushes up the cost of imports.
Sales of household goods fell 7.3% in December, the biggest drop since January 2010. Food sales fell 0.5% last month.
IHS Global Insight chief UK and European economist Howard Archer said: "The major problem facing the economy - and retailers in particular – is that it looks inevitable that the fundamentals for consumers will weaken markedly as 2017 progresses with purchasing power being increasingly squeezed. We also suspect that the labour market will soften."