@tsarstepan,
												A yum yum is a type of glazed doughnut.  It’s hard to see how a hybrid could exist unless it’s the shape.  Yum yum s are usually square or rectangular, not circular.
It’s M&S trying to be cheeky, make little kids laugh.  M&S is a prestige brand that has been losing customers in fashion.  It’s increasingly being associated with old people, and they certainly do dominate.
The food however is of a very high standard, always been held in high regard.  I stop off for food but I don’t bother with clothes.  Their cheese scones are really good.