According to CBI's latest Distributive Trades Survey, 39 per cent of retailers saw sales volumes fall in September, with 24 per cent seeing them rise year on year.
The three-month moving average sales, which smoothes out volatility in the monthly figures, also declined (down 11 per cent), at the fastest rate since August 2009.
Sales were reported to be poor for the time of year by a balance of -30 per cent of retailers. The decline in volumes was felt across almost all of the main sub-sectors: furniture was down 59 per cent, department stores down 46 per cent, clothing down 36 per cent and footwear and leather down 15 per cent.
Grocers' sales were broadly flat - down three per cent.
Sales volumes are expected to decline at a similar rate for next month (down 14 per cent).
"High Street sales are sluggish, but appear to be stabilising," said Judith McKenna, chair of the CBI Distributive Trades Panel and Asda COO. "Shoppers are still clamping down on discretionary spending and focused on buying the basics at the best price.
"With the consumer squeeze set to get tighter with the winter utility bills rise, we expect retailers will face a challenging October."