It grew by 2.2% for most of the month and though the overall rise was 4.2%, this was skewed by a four-day period flattered by comparisons with a spell depressed by heavy snow last year.
Spending had grown by 3% in November and 2.9% in the run-up to Christmas.
January's slowdown was blamed on the continuing fall in real wages, with pay lagging behind inflation.
Spending on utilities was down 14.8%, with less energy as the weather was milder this year, while supermarket spending was off by 1.7%.
Restaurant spending was up by 16.6%, for women's clothing it rose by 11.3%, and hotels saw a rise of 8.9%.