Morrison's often aren't that good for what I call "cheapo chuckouts". They tend to only give quite small discounts (e.g. from £2.49 down to £2.19) for many hours and then, if the products still remain on the shelves, reduce them a bit more (e.g. down to £1.79 in my example).
The Co-Op (or. at least, our local co-operative society) are actually quite good for discounts, immediately giving a full 50% off everything which they put a yellow sticker onto.
Asda tend to start by offering small discounts but then, if products remain unsold, putting more and more yellow stickers on (with ever greater discounts). So I've seen £4 roast chickens reduced to 50p and big sacks of spuds offered for just 20p.
Tesco work on a similar basis but they don't seem to use as many yellow stickers. A £1.75 sarnie will initially be offered at, say, £1.35 but then, if still unsold, might dramatically drop to 10p.
Sainsbury's are among the best for giving significant reductions quite quickly.