The mark ‘Firth Brearley Stainless’ would suggest that this knife was made in the early 1920s.  Since the name ‘O. Walker & Sons’ was not listed in any Sheffield directory, it is likely that the knife was manufactured in Sheffield for a retailer.  A strong candidate is Oswald Walker & Sons, a wholesale dealer in cutlery and electro-plated goods, which was based at Bradford.  The founder was Oswald Walker (1861-1935), who had been born at Thirsk and first traded in Whitby jet ornaments.  Besides selling cutlery, he was also known as a Wesleyan Methodist preacher and pigeon fancier (Yorkshire Evening Post, 20 April 1928).  After his death on 17 October 1935, aged 74, the business was operated by his sons, Oswald, John Edward Laws, and George Lockey (Yorkshire Post & Leeds Intelligencer, 19 October 1935).