The volume of textiles, clothing and footwear sold in the UK fell 4.2% in December compared to the year before, according to the Office for National Statistics.
Clothing and footwear sales were down 6.2% on November - the largest monthly fall on record - reflecting the mild weather and shift towards buying discounted goods on Black Friday.
The average amount spent on clothing and footwear decreased by 3% year on year, while average prices fell 0.9%.
Across the entire retail industry, the volume sold in UK shops rose by 2.6% year on year in December. The total amount spent fell by 1%, while average store prices (including petrol stations) fell by 3.2% year on year.
The value of online sales was up 8.2% on 2014, but down 5.2% on the previous month.