This is a new reproduction of the 3-pocket magazine pouch that was commonly used by British and Canadian officers and other ranks during WWI for the Colt automatic in either .45 ACP or .455 Colt.  Originals are nearly impossible to find. The belt loops are wide enough to fit over a standard Sam Browne belt ( 2 1/4 inches).

This style pouch was also adopted by Norway after WWI.

See my other listings for the matching holster for the M1911 Colt pistol.