2nd Pattern Fairburn-Sykes Fighting Knife variant.
This example of the Second Pattern has several unusual features chiefly the chunky and bulbous hilt. The grip has very deep and coarse knurling compared with the standard Second Pattern. Flook suggests that there is some evidence to link this pattern of knife with the Marines, SBS and Commandos of 30 Assault (SEE British & Commonwealth Military Knives by Ron Flook).
This example is in good overall condition with a stained and sharpened blade and is contained in a scabbard that has had the top section removed. No obvious markings. An uncommon variant.