Marks & Spencer (MKS.L) will rejoin Britain's FTSE 100 (.FTSE) stock index after a four-year hiatus, it was confirmed on Wednesday, capping a return to fashion for the food and clothing retailer after years of failed turnaround efforts. Before its 2019 ejection, the food, clothing and homewares retailer, known affectionately as "Marks and Sparks", had been a member of the blue-chip index since its launch in 1984.