This knife has a combination blade for cutting wire, stripping insulation, and filing terminals.  This marks it as an electrician’s or wireless knife – a design that was popularised in the interwar years.  The ‘maker’, though, is difficult to identify.  ‘Myatt’ was a name that appeared rarely in Sheffield directories – certainly not as a cutlery manufacturer.  One possibility is that the knife was factored (‘bought in’) from Sheffield by W. J. Myatt & Co Ltd, the well-known Birmingham silverware manufacturer.  The founder was William James Myatt (1860-1937), who established the company in 1897.  He registered a silver mark in Sheffield in 1906.  In the 1920s, Myatt marketed his own brand of safety razor (Birmingham Gazette, 26 June 1926).  His connection with Sheffield must have been close: William P. Deakin (James Deakin & Sons) was once chairman of Myatt’s.  After the War, Myatt’s manufactured electro-plated and pewter wares and became involved in light engineering.  The company was liquidated in 1973.  For a brief account of its history, see John Culme, The Directory of Gold & Silversmiths, Jewellers and Allied Trades 1838-1914 (1987).