Marks & Spencer revealed its beleaguered clothing arm suffered its worst sales performance for more than a decade as it cut back on promotions amid a "weak market".
The retail giant posted an 8.9% plunge in first quarter like-for-like sales in its clothing and home division - marking the biggest drop since the April to July quarter in 2005.
Chief executive Steve Rowe - who took over from Marc Bolland in April - blamed the worse-than-expected sales fall on moves to reduce promotions and shift its summer sale into July as part of his turnaround strategy.
He said it was also hit by a "weak market" amid pre-Brexit vote jitters on the high street, while the timing of Easter wiped around 0.8% off clothing and home sales growth.
Mr Rowe said: "Consumer confidence weakened in the run-up to the EU referendum.
"While it is too early to quantify the implications of Brexit, we are confident that our strategic priorities and the actions we are taking remain the right ones."
He added shopper confidence remains "fragile" after the Brexit decision.
"We are operating in uncertain times," he warned.
The sales fall was far worse than expected and sent shares down as much as 2%.
M&S has already lost a third of its value on the stock market in the past three months amid worries over its overhaul and as retailers suffered heavy share falls in the immediate aftermath of last month's vote to leave the EU.
Mr Rowe said they were "not the numbers I want to see" for first quarter trading, but added they were "the numbers I expected to see" after the group axed 28 promotions under a plan to instead lower every day prices.
The shift in promotions reduced like-for-like clothing and home sales by 5%, according to M&S.
The group's food arm fared better, with like-for-like sales down by 0.9% in the 13 weeks to July 2, of which 0.5% was due to Easter timing - while total comparable UK store sales were 4.3% lower overall.
Mr Rowe warned when unveiling his overhaul strategy in May that there would be no quick fix in the battle to revive its beleaguered general merchandise business.
He pledged to cut every day prices for nearly a third of its clothing ranges, while boosting staff numbers on the shop floor.
At the heart of his revamp is a plan to win back ''Mrs M&S'' - its once loyal army of women shoppers aged 50 and over, who he said have been ''neglected'' in recent years.
The plans received a lukewarm response on the stock market.
But he insisted, on unveiling first quarter figures, that the group was "doing the right thing".
"We knew our actions would reduce total sales, but we are seeing some encouraging early signs," he said.
It has cut prices on around 1,000 lines since January and reported sales up by as much as a quarter on some of these products.