Retail like-for-like sales in November fell 1.6%, the weakest performance since May.
Total sales edged up 0.7%.
Non-food sales continued to decline as clothing and footwear sales were hit by the mild weather.
Non food non-store sales growth slowed, rising 8.6% - the weakest growth rate since March.
British Retail Consortium director general Stephen Robertson said: “There’s a worrying lack of cheer in these figures. The weakest increase in sales for six months suggests consumers are keeping a tight rein on their spending, despite Christmas being so near.
“This November’s mild weather contrasted with much lower temperatures last year, hitting sales of winter clothing and footwear particularly hard.
“Consumers are not quite in the Christmas mindset yet, although stores are working to generate much-needed sales with high levels of festive discounting.
“Retailers hope that customers who’ve managed their finances carefully in recent months will still treat themselves and their families in December, unhampered by the severe weather which disrupted shopping twelve months ago.
“The Autumn Statement’s bleak assessment of the UK recovery is the latest in a sequence of poor economic news which includes falling sales, rising unemployment and stubbornly high inflation.
“The Chancellor offered some modest assistance but, this close to Christmas, more concrete progress on measures to inspire confidence in consumers and businesses is badly needed.”
KPMG head of retail Helen Dickinson said: “The latest figures prove once more that the health of UK retailing is deteriorating.
“Christmas is a crucial trading period for the UK retail sector but this year many retailers will be nervous and unsure as to how the season will pan out. Cash-strapped consumers continue to be reticent and last week’s gloomy economic forecast by the Chancellor won’t help to boost confidence levels.
“Any sales are hard won, with high discount and promotion levels. Retailers’ performance is suffering because of weak top-line growth and declining margins, making the backdrop even more challenging. December will require some tough decisions for a number of retailers as they struggle to plot a path in such challenging conditions.”