Although similar in appearance to modern cables, these have conductors primarily comprised of aluminium.
This type of cable was used for a short period in the 1970s. The cores are aluminium with a copper plating.
It is unusual to find cable of this type, as most of it should have been replaced by now.
It's only advantage was reduced cost during a brief period of very high copper prices.
Although the cores have the appearance of copper due to a thin plating, when cut the ends will be bright silver.
The example here has been scratched with a sharp knife, revealing the silver coloured metal underneath (black insulated core).
The cable is substantially lighter than the copper equivalent and much softer to cut and bend.
This cable is no longer listed in BS7671 and information about it's current carrying capacity is difficult to obtain.