Just doing a bit of tidying up on some older threads, mainly for the benefit of anyone searching the site for information.
Yes, that’s a silver plate mark, not a hallmark. There are several possibilities for a ‘W.M’ mark, but that one with the gothic ‘E’ and ‘P’ (for Electro-Plate) is generally attributed to William Marples & Sons of Sheffield.
Founded in 1828 by William Marples, it became “William Marples & Sons” in 1860 when Edwin Henry Marples and William Kent Marples joined their father’s business and continued under that name (later becoming “Ltd”) until purchased by W. Ridgeway and Sons and C. and J. Hampton in 1962.