Is the buried cable mechanically protected from the type of damage it could reasonably be subjected to? If yes, no code, if no, C2.
I'd argue for example that if a non-armoured cable was buried 600mm deep in a garden in a robust duct that would deter a hefty blow from a shovel then the regulations have been complied with and there is no potential danger, however in a car park, where it's likely at some point there will be a 360 digger poking around in the ground, then the regulations likely haven't been complied with and this cable does pose a potential danger.