Tricky Dicky wrote:

I am looking to use some 50mm X 50mm trunking around the garage to
take mains wiring. I would also like to run some Cat5e cables in the
trunking but I cannot find any that will take a separator and was
wondering if it was acceptable to install smaller trunking within the
larger one and enclose the low voltage cables within?

If you don't want to use the larger dado trunking, can't see why
trunking within trunking wouldn't be acceptable.