Why HMS Vanguard kept sextuple Bofors mounts

Why did HMS Vanguard retain sextuple Bofors mounts instead of receiving American twin 3-inch Mark 33 mountings?

Cost and the sextuple Bofors' effective volume of fire are cited, with national pride suggested as another obstacle to an American replacement.

Cost is the first reason offered for retaining Vanguard's ten sextuple 40 mm Bofors mounts. The mounts supplied a heavy volume of fire and are judged to have worked well once fully developed. The proposed replacement is the American twin 3-inch Mark 33 mounting, which the panel distinguishes from the British 3-inch guns carried by the Tiger class. National pride is also suggested as a reason Britain would have resisted fitting an American system to its last battleship. The subsequent STAAG discussion concerns a separate mounting with its own radar and stabilization equipment.