The clothing to food retailer said that it would trial an offer of around 350 'must have' branded products in 19 stores in Tyneside and Teeside.
The offer would represent around 7% of its range and would include products such as Marmite, Heinz Tomato ketchup, household products and toiletries.
Like-for-like food sales for the year to 29 March dropped 0.4%, and by 0.5% for the fourth quarter.
Market share had hit 4.3% and M&S said it planned to target market share of 5% by opening more Simply Food stores, enhancing products and services in larger stores, and ensuring everyday key product lines offered better value.
M&S also warned market conditions would remain difficult and it had failed to meet internal bonus targets set in April 2007.
“We expect market conditions to remain difficult for the foreseeable future and are managing our business accordingly,” said CEO Sir Stuart Rose. “Tight stock control and management of costs are a priority.”