Could Britain manufacture new Challenger 3 hulls?

Can Challenger 3 only be created by upgrading Challenger 2, or could Britain build new hulls?

New hulls could be built if Britain paid to establish the necessary factory.

New hulls would be possible if Britain paid to establish a factory to build them. The constraint is the investment needed to create production capacity, rather than an absolute requirement to convert existing Challenger 2 hulls.