There is no armouring on this cable, the concentric wires are the actual neutral and earth conductors. This cable is fine for the DNO's as the terminations and spreading of the conductors are hidden within the cut-out. It's a different matter for termination into standard electrical components (CU's/DB's and the like), and unless you know what your doing, can very easily end up looking like an amateurish pigs ear of a job!! The best and easiest solution is using a 3 leg heat shrink breakout and heat shrink tubing for the gathered concentric conductors.
The only way i would ever use this type of cable for underground installations, is within a heavy duty (thick walled) PVC duct, buried at a suitable depth. Which by the sounds of it, is what your going to have to do, if your going to use the customers cable!! Never install this type of cable in a direct buried situation.... Apart from anything else, it won't conform to the requirements BS7671...