Brabazon was a government programme, postwar reconstruction and all that. It just developed such inertia that it could not be cancelled, despite Bristols wanting to pull the plug. The Brab was assembled alongside the servicing of Connie's, which were already doing the transatlantic route, in the adjacent hangar bay. Embarrassing.
The Britannia was I think private enterprise and certainly used lessons learned from the Brab programme. Alas it was delayed by icing problems in the Proteus engine ironically caused by the requirement for a very short engine to be mounted within the Brab leading edge.
I once saw both aircraft fly over our house in formation, G-AGPW and G-ALBO if I recall correctly.