Earthing or bonding ?

Now we are really getting into trouble! An exposed conductive part is (BS7671): Conductive part of equipment which can be touched, which is normally not live but could become so under fault conditions.

Now the sheath plastic is not conductive, so it fails this test, whether it is "adequate" insulation for 230V (which it is). Now consider metal plumbing which is bonded to the installation MET. Is this an exposed conductive part? No because it is not part of the Electrical installation, although it is connected. SWA is not considered an Exposed Conductive Part.

Now the actual question, which is slightly confused. Are you asking if the SWA armour is an Earthing conductor under your conditions, then yes. If it is only connected one end then No. Even if you put an Earth G/Y cable alongside an SWA, the armour can still act as an Earthing conductor too, the current will share all the parallel conductors depending on the resistance of each.

It is not a requirement that Earth or CPC conductors are sheathed, although they should be marked at the ends if not. The SWA sheath PVC is exactly the same as wire insulation, although it may be thicker, but it is only there to prevent corrosion of the wires. Look at trunking and conduit. As much SWA is 90 degree XLPE the same applies, the sheath is insulating. Whilst on that point, sometimes Insulated and sheathed cables get the name "double insulated" Whilst this is true, the sheath is classed as mechanical protection, because it could be damaged and the double cannot be guaranteed. The same goes for SWA but even if exposed the armour is not dangerous under any normal conditions and the likelihood of contact (buried for example) is effectively zero.

David Stone said:

Now the sheath plastic is not conductive, so it fails this test, whether it is "adequate" insulation for 230V (which it is).

It is not ... the sheath, conductive or otherwise, is there for mechanical protection only. It has no defined electrical properties and these are not tested in cable standards.

David Stone said:

It is not a requirement that Earth or CPC conductors are sheathed,

David, if the armour is earthed at one end of the cable, and ADS is used, equally easy to argue it's not a cpc, because it's not connected downstream, and cpc's are to be run to each point in wiring, and be part of, or installed adjacent to, the wiring system containing the live conductors.

David Stone said:

It is not a requirement that Earth or CPC conductors are sheathed,

David, if the armour is earthed at one end of the cable, and ADS is used, equally easy to argue it's not a cpc, because it's not connected downstream, and cpc's are to be run to each point in wiring, and be part of, or installed adjacent to, the wiring system containing the live conductors.