The retail chain British Home Stores was founded in 1928, so at least since then.
I wasn't aware until now that this is considered an Americanism
BHS was founded by by a group of U.S. entrepreneurs, however, it is generally accepted usage to refer to various retail spaces as shops or stores synonymously. Some even use it as their brand identity e.g. The Body Shop, The Gift Shop, The Tie Store and now defunct Army & Navy Stores et al.
Nevertheless, there are certain distinctions to be made, i.e. when someone says 'I am nipping out to the shops - do you want anything?' usually means a visit to small local independent shops/convenience stores, colloquially referred to as corner shops (bodega/deli) situated on the High Street and not mean Harrods, albeit it might also qualify as a local shop for some of the residents in Knightsbridge.
I wasn't aware until now that this is considered an Americanism.