Associated British Foods blamed a fall in shopper numbers and unseasonably warm weather for negative underlying sales at its Primark fashion chain in November, sending its shares lower.
Shares in the group, which also has major sugar, grocery, agriculture and ingredients divisions, fell by as much as 3.3% today.
The update on Primark added to evidence of a slowdown in British consumer spending in the run-up to Brexit.
Industry data published this week showed British consumer spending grew last month at its slowest pace in more than a year, excluding Easter distortions.
Online Black Friday sales also failed to offset a lack of confidence about the economy.
In a brief trading update published ahead of its annual shareholders' meeting, AB Foods said the group's sales and profit for the first eight weeks of its 2018-19 financial year, which began on September 16, were in line with expectations.
However, it said that during November Primark's trading "was challenging, in a tough retail market."
Finance director John Bason told Reuters Primark's like-for-like sales were "just positive" in September and October but were negative in November. He declined to give precise numbers.
"This isn't a call on Christmas - we've got three big weekends coming up now before Christmas. But I think it is a call on quite mild weather during November and I think it's affected footfall," Bason said.
"It's a blip that from a profit perspective we can manage," he said.
He said that with careful inventory management and improved margins, the group's expectation for an increase in Primark's full-year profit was unchanged.
Primark, which accounts for about half of AB Foods' revenue and profit, currently trades from 363 stores in Europe and North America. It trades as Penneys here.
AB Foods maintained the overall guidance it issued last month - group adjusted earnings per share for 2018-19 in line with its 2017-18 outcome.
