John Lewis blamed the economic crisis for a 14 per cent decline in sales last week, its worst performance this year.
Most stores across the country registered falls, with the biggest a 16 per cent drop at the retailer's Peterborough site.
Sales at Waitrose, the group's premium grocery chain, were also lower by 4.6 per cent, adding to the gloom.
London shoppers made a return, however. Oxford Street sales were up 2.1 per cent over the week.
Head of selling for John Lewis, Barry Matheson, said the stores are in "fantastic shape".
"However, we are not immune from the reality of the economic crisis that grasps every headline, and that is reflected in last week's result," he added.
Howard Archer, from Global Insight, said: "Given that John Lewis' department store sales are seen as a good bellwether for the health of consumer spending, the recent sharp year-on-year declines in sales reinforces belief that consumer spending is significantly weaker than is portrayed by the retail sales data from the Office for National Statistics."
The ONS reported retail sales volumes were only down by 0.1 per cent month-on-month in October and were up by 1.9 per cent year-on-year.
The retailer highlighted its haberdashery sales, particularly in sewing machines, and new technology such as the e-Book Reader.
John Lewis said it is expecting technology products to perform well in the run-up to Christmas.
However, technology sales were down 12 per cent and homeware sales plunged 18.7 per cent last week.
Remaining optimistic, Mr Matheson added: "The newspapers are full of stories about the impact of the credit crunch spreading to the real economy, and retailers are frequently being cited as evidence of that.
"But that in no way diminishes my conviction that we will once again outperform the competition as we get closer to Christmas."