A common Commonwealth close-in weapon

Would a non-declined British Empire and Commonwealth develop a Phalanx-type weapon?

Probably, but as a shared 30 mm system or common family rather than separate national weapons.

Britain, Canada, and the other partners would likely develop a common weapon rather than parallel systems. A 30 mm design is plausible even if local producers give it different names. The same collaborative logic could support a vertical-launch successor to Ikara. Standardisation and pooled development suit an integrated defence structure.