I agree with so much of the above, especially concerning T-shirt length. I don't wear skirts, so have no axe to grind there.
Jumpers, though - can we please have them just slightly longer. I don't want 'longline' ones, covering my bottom, as that just accentuates my size, but I would like them to reach below my hip bone, so that when I reach up or move around they don't part company with my (waist high) trousers.
Also, I wish they still sold the lovely stretch cotton trousers that I bought for several years.
And yes, as mentioned, STOP trying to appeal to the youngsters - they would die rather than admit to shopping in M&S. Their target audience should be age 40 and over (maybe even 40 is too young these days...)