No CPC continuity at all in a domestic garage fed underground from the main house. Loss of continuity caused by a) loose gland nut on an SWA termination into a steel surface box. It was impossible to tighten the locking nut because the back box lug fouled the nut! b) the gland to steel box termination at the other end was corroded so no connectivity at all between the back box and the gland. Even if there was no corrosion present then there was no fly lead between the back box and the circuit CPC, co the connectivity would have relied on the front plate (plastic 13A socket outlet) screws only. The front plate screws were corroded and had extenders as well. Re terminated the lot using lug rings on the glands for the fly leads and suitable back boxes. The wiring had been previously untouched for probably 20 years or maybe 30 years like that. Including a CU change probably around 10 years earlier. I spotted the problem when an extra socket was required in the garage.