The British have wanted to go to a .280 even back to the early 20th century. There was never anything wrong with the caliber, it was just world events etc. which kept them from going to it.
I think you are right about them wanting it again in the 1950s but it was the .308 which we forced on them, not the .223.
You are probably right, just remembered them being forced into something back when. Probably liked to my reading that the FNLAR was originally designed for a lighter round than the .308, maybe this .280.