Hi,
Welcome to the Forum.
Firstly, it's not a hallmark. A hallmark is a mark struck onto precious metals by an official assay office. What we have here is a maker's mark only.
The maker was William Hutton & Sons of Sheffield, see:
http://www.925-1000.com/silverplate_H3.htmlThe 'crossed arrows' mark was originally the trade mark of the Sheffield firm of T.& J. Creswick, they first registered the mark in 1811. In 1902 this business, now styled Creswick & Co. and their trade mark, were acquired by William Hutton & Sons Ltd. Hutton's themselves were acquired by James Dixon & Sons Ltd. in the early 1930's.

William Hutton & Sons Ltd. - Australian trade mark registration
The 'BP' marks stand for 'British Plate' a name used by Hutton's for their particular form of plating. The 'A1' mark is their quality indicator, ie, their best quality.
Trev.