M&S jeans are variable from one hanger to the next; I found the jeggings were big on my thighs and massive on the back waist, but were uncomfortably tight on the calves.
Primark, however, are great. Just wish they were available now. And that they did more high waisted over the flab ones.
There is one trick, though - if you get standard length but 7/8 design, they are perfect full length for a 27-29" inside leg.