The spike bayonet used with the No4 bayonet was a pretty basic design, being in essence a forged 6 inch metal spike. Despite its simplicity, during wartime even simpler and cheaper construction methods were always sought and in the case of the bayonet one firm, Joseph Lucas Ltd. of Birmingham, managed to create an economy version of this already simple bayonet:
The bayonet used the same scabbard as a normal Mk II pattern spike bayonet:
The Mk III bayonet used seven fabricated parts welded together to make the socket, rather than a single machined casting. This results in the socket having a crude, unfinished appearance:
This had the advantage of being quicker and cheaper to manufacture and did not require extensive machining operations so less skilled operations were needed in its manufacture. Despite the crude appearance, however, it was still just as functional as a normal bayonet. The crudeness becomes very apparent, however, when it is placed next to a normal Mk II bayonet:
196,200 of these bayonets were produced by the company during the war and although they were fine as a wartime substitute, once war ended they were quickly dropped and declared obsolete in 1946. Today, thanks to the small number of the bayonets originally produced, they are significantly rarer than the more usual Mk II. Despite this rarity they were largely overlooked by most collectors until recently due to the crudity of their construction. Interest has, however, grown in recent years and they are now starting to fetch prices rather higher than the Mk II.