It is a Phrobis Modular Field Knife (MFK). They originally came with three interchangeable cross guards. The pommel/tang screws off allowing the grip to be removed. You can then easily install any one of the three crossguards. The tang on this knife is plastic which didn't make for the strongest knife in the world.
The MFK blades were made by Marto. The very early ones had no markings indicating that; later ones were marked "Made in Spain". Same for the Phrobis CUK (Combat Utility Knife).