I confirm the assay office and date as Birmingham, 1891, but the sponsor's mark does not seem to match the published mark for Arthur Downing Ltd. Your mark has what appears to be a hyphen as well as a stop between the letters.
Hello both, Date letter looks to be the gothic 'x' instead of gothic 'r' I think the date is for 1897/98 and the makers mark is Arthur Downing registered as a Goldsmith and Jewellers at 25 Upper Hockley St, Birmingham. 1st registered 12 October 1883. Unusual to see both a hyphen and pellet in the same mark. Hope this helps. kind regards Craig