It is electroplated so neither silver nor sterling. The gothic lettering reads EPBM - electroplated Britannia metal; Britannia metal is a base metal alloy. The second letter of the manufacturer’s initials is obscured but the whole thing is probably HE&Co for Hawksworth, Eyre & Co, a Sheffield company.
Treat it like silver for cleaning, with a good quality silver polish - the surface of electroplate is pure silver but the thinness of the coating means that a non-abrasive polish is best.