The high street giant confirmed the savings in a trading update to the City today.
M&S has tested a series of pilot stores with the new look and will now roll out the refurbishment programme between now and the middle of next year.
The firm said: “Having thoroughly tested the new concepts, and by focusing on strong management of capital investment, we now plan to roll it out to the remainder of our estate, with no reduction in scope, for £100m less than the previous guidance of £600m.
“Our target completion date for the roll-out by mid 2013 remains unchanged.”