There probably is such a regulation. However, as I said, I presume that those who wrote 522.8.10 must have believed that there are some non-armoured cables which have an earthed screen and which are suitable for direct burial, otherwise they would presumably not have mentioned it as an acceptable option for directly buried cables (not in conduit or ducts).I'm sure there is a reg somewhere about cables having to be suitable for the environment where they are used. Would you bury BS8436 cable directly in the ground and then claim that you had exercised reasonable skill and care etc?
Kind Regards, John