It will close about 30 full line UK stores and change around 45 stores to only sell food. Other stores would be re-located.
The cost of the programme would be £50 million for the next three years, rising to about £100 million pounds in years four and five.
M&S also plans to focus its international business on a franchise model, exiting its loss-making owned business across 10 markets - at a cost of £150-200 million over the coming 12 month period - eliminating annual losses of 45 million pounds.
M&S also reported an 18.6 percent fall in underlying pretax profit for its first half to October 1 of £231.1 million pounds along with a 2.9 percent fall in second-quarter underlying clothing sales.
Like-for-like food sales were down 0.9 percent.
The overhaul, led by boss Steve Rowe , will also see big changes to what is sold in stores.
More space will be given over to the chain's food halls, at the expense of its struggling general merchandise division, including clothing.
Some branches will be converted to food only. Insiders stressed the move would not lead to large scale job losses, with Mr Rowe having already pledged to grow the number of store assistants.
It comes as Mr Rowe is expected to announce plans to slash its number of overseas stores.
Reports say the firm will confirm it is shutting 10 stores in the Far East, along with a flagship branch on Paris's famous Champs-Elysees.
It comes as Next is poised to reveal another slump in sales next week.
Analysts predict general merchandise sales fell 3.9% in the six months to October, while food sales were flat.
Profits of around £216million are predicted. M&S said it would not comment on "rumours or speculation".
In July, M&S announced its clothing arm suffered its worst performance for more than a decade as it cut back on promotions, with sales plummeting 8.9%.