This for those of us who remember an M&S face product from before the pandemic. It was in either the 2018 or 2019 Advent calendar. It was a gel product that gently exfoliated your skin by forming little balls of product and dead skin cells when you rubbed it on your face. It worked brilliantly as a gentle but effective exfoliating technique and watching the little grey balls form was very satisfying. M&S never stocked the product again...
I've found a good replacement. Beauty of Joseon Apricot Blossom Peeling Gel. It works in exactly the same way, and my sensitive skin does not react to it. It leaves my skin perfectly smooth without irritation. It is drying and you'll probably need a good moisturiser.
It is available online through various retailers.