BBC business editor Robert Peston said the announcement was significant as it meant M&S would be placing far fewer orders than planned with other businesses.
"That's a graphic illustration of how the horrors of the financial economy are infecting the real economy," he said.
Sir Stuart told the BBC: "We are being a little bit prudent."
"Customers are being thoughtful about expenditure but that's hardly surprising in the world we live in today. We'll cut our cloth according to our means."
Despite the sales slide, M&S's shares jumped on the London market. Analysts welcomed news of the cost cuts and said the sales performance was in line with expectations.
M&S shares closed up 8.1%, at 227.25p.
International sales up
Like-for-like general merchandise sales - which includes clothing - were down 6.4%, while food sales were down 5.9%.
M&S SECOND-QUARTER SALES
Group sales up 0.4%
UK sales down 1.6%
UK like-for-like sales down 6.1% (General Merchandise -6.4%; Food -5.9%)
Online Sales up 34%
International sales up 24.2%
Sir Stuart highlighted that looking at total sales, as opposed to like-for-like, gave a slightly different picture. Like-for-like sales exclude the impact of new stores.
"Our food sales are broadly flat in total, because we've been opening some stores, and in clothing the numbers are down about 3% in total terms," he said.
Overall group sales were up 0.4%, with UK sales down 1.6%. However, there was a 24.2% rise in international sales and a 34% rise in online sales.
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