This is a "spike" bayonet (falling into the "socket" category) used on the No.4 SMLE (Short Magazine Lee-Enfield) Infantry Rifles used from about 1939 to about 1957 (perhaps into the 1960s); it was the successor to the P1907 Mk1 Bayonet and the predecessor to the No.9 "Knife" Bayonet. It has no proper handle but home guards were issued these with a "broomstick" attachment that allowed them to be used - with this extension - as a close-combat thrusting weapon.
They are very basic, yet very functional as a bayonet (useless as a knife). They come in a number of variations, some being produced by Savage Arms in the United States. These were produced in very large quantities and the common MkII variant sells on the current retail market for under $15 with scabbard; the MkI "Grooved Spike" is quite scarce and will bring considerably more (watch for fakes).

The scabbards are cast metal or sometimes plastic (Victory Plastics).

These bayonets were also used by Australia, Canada, New Zealand, and perhaps others.