Like-for-like sales fell 2.6% and total sales fell 0.4% in November, according to the British Retail Consortium today.
The BRC said it was the first time its sales monitor had shown two consecutive months of declining total sales.
October sales showed a decline of 0.1%. The monitor began in 1995.
The BRC said the food and drink sector was the only sector to show sales up on a year ago.
It said, despite extensive heavy discounting, clothing and footwear, furniture and big-ticket homewares fell further below year-earlier levels.
It said discounts and promotions continued but often failed to tempt customers unless they perceived value or really needed the product.
Non-food non-store sales in November were 9.5% higher than a year ago.
As with store sales, this was worse than in October, when sales were 16.6% up on a year ago.