Bob Minchin formulated the question :
I could be wrong but had always assumed the requirement was based on the need
for separation between power and data to reduce
interference/inductive/capacitive coupling.

IEE Regs do not care about that, but it states something about the
insulation of the lower voltage cables has to be to mains spec.. Data
cables are not rated for mains voltages, so there has to be some sort
of physical barrier separating them. I would imagine that the data
cable in its own trunking would be OK.