3 phase up the one conduit

[davesparks]

Now, does anyone know where in the regs it indicate no signage is required for 440v running conduits ?

Presumably you mean a standard UK nominal 230V/400V rather than 440V? If so then warnings are not required anywhere as the nominal voltage to earth does not exceed 230V

If it is a non-standard nominal 440V supply then you may need to consider suitable warnings if it is somewhere where you would not normally expect to find it.