The retailer said that around 60 clothing and home stores so that it can focus on food.
It comes as they announce an 18.6% plunge in underlying half-year profits to £231.3 million while bottom-line profits crashed 88.4% to £25.1 million.
Chief executive Steve Rowe also outlined plans to shut 53 stores across 10 international markets – including 10 in China and seven in France, while pulling out of Belgium, Estonia, Hungary and Lithuania – putting around 2,100 jobs at risk.
M&S said it will close around 30 of its 304 full-line stores – selling clothing and home as well as food – and downsize or replace around 45 shops to Simply Food outlets.
It will also relocate some other outlets, while opening other stores in so-called under-served areas.
The group remained tight-lipped on the number of UK staff impacted by the plans, but said that, where possible, it would keep ‘job continuity’ for affected employees.
The group insisted it would have more stores overall after the revamp, with already-announced aims to open more than 200 Simply Food outlets by the end of the 2018/19 financial year.
Mr Rowe, who took over from Dutchman Marc Bolland in April, said: ‘Over the next five years we will transform our UK estate with around 60 fewer clothing and home stores, whilst continuing to increase the number of our Simply Food stores.
‘In the future, we will have more inspiring stores in places where customers want to shop.’
He added: ‘These are tough decisions, but vital to building a future M&S that is simpler, more relevant, multi-channel and focused on delivering sustainable returns.’
The latest restructure moves come as M&S revealed more sales falls in its embattled clothing division, with like-for-like sales down by 5.9 per cent in the first half.
But it narrowed the sales decline from 8.9 per cent in the first quarter – its worst performance for a decade – to 2.9 per cent in the second quarter.
Same-store food sales fell 0.9 per cent over the half-year, while it saw growth of 0.3 per cent at M&S.com, leaving overall UK like-for-like sales 3 per cent lower.
He said: ‘Over the next five years we will transform our UK estate with c.60 fewer Clothing & Home stores, whilst continuing to increase the number of our Simply Food stores.
‘In the future, we will have more inspiring stores in places where customers want to shop that complement our growing digital offer.
‘Internationally, we propose to cease trading in ten loss making owned markets, but intend to continue to develop our presence through our strong franchise partners.
‘These are tough decisions, but vital to building a future M&S that is simpler, more relevant, multi-channel and focused on delivering sustainable returns.’