Shares at Marks and Spencer have slumped after it reported a 5.3 per cent decline in like-for-like sales for the first quarter.
As of 11:00 BST shares at the retailer had fallen by 24 per cent.
Earlier M&S said sales were down 4.5 per cent in food and 6.2 per cent in general merchandise, blaming low consumer confidence.
M&S said it is taking steps to meet the challenging market conditions, and announced its food director Steven Esom is stepping down to be replaced by John Dixon, currently head of the company's home and M&S direct divisions.
The company's high-end food business faced competition from other retailers over the quarter and suffered from consumer belt tightening, M&S said.
Chairman Stuart Rose said: "At our preliminary results in May, we reported a mixed start to our 2008/9 financial year and expressed caution about consumer sentiment.
"Since then, consumer confidence levels have deteriorated markedly and market conditions have become more challenging."
Although general merchandise and food were affected by the market conditions, clothing, home and M&S direct have all increased sales levels, leading to the management shake-up.
"Four years ago, M&S was a weak business in a strong market. Today, we are a strong business in a weak market," Sir Stuart added.
Market conditions are set to "remain difficult" the retailer warned.
M&S said its summer sale would go ahead at the normal time, and said its guidance on operating costs had not changed.