The armour as CPC for SWA is not obvious. It usually has larger CSA than the conductors but as it is steel the resistance is around 8 times higher per mm^2. For smaller cables it is often adequate, better in fact than T&E for R2, but for large cables it can fail the adiabatic requirements so you may end up using 3-core for single phase, 5-core (expensive) for three-phase, or running a supplementary CPC of 0.5-1.0 phase size alongside.
The last page of this data sheet has the info you might be looking for: