M&S, like other UK retailers, has faced tough trading in recent times
Marks and Spencer is to hold a one-day, 20%-off sale on Thursday, a move that analysts see as a sign that the retailer is continuing to struggle.
The move will see M&S go head-to-head with Debenhams in an effort to entice customers after dismal October trading.
Department store group Debenhams began a three-day sale on Wednesday, with prices cut by up to 25%.
The one-day sale is the first M&S has held in four years. M&S recently posted a 34% drop in six-month profits.
Several other large retailers are thought to be planning pre-Christmas sales of their own and Philip Green's Arcadia fashion group - which includes Burton and Dorothy Perkins - is also likely to start a sale this week, according to analysts.
The decision to hold pre-Christmas sales is unusual as such discounts are traditionally seen after the festive period. Debenhams is the exception and has occasionally held sales before Christmas.
The downturn in the economy, worry about future job security and plunging house prices have all led to consumers tightening their belts and cutting down on non-essential spending. This has hit higher-end retailers hard as consumers turn to cheaper, discount stores.
UK retailers are thus bracing themselves for a difficult trading period in the coming months.
Debenhams chief executive, Rob Templeman, said Christmas 2008 would be more competitive than last year. He added that an increase in unemployment would further hurt retailers.
"My worry is unemployment. It's forecast to be three million next year. I wouldn't be surprised if it's more than that," he said.