Will unshielded Cat5 cable run in same boxed skirting as mains cables be OK so long as it maintains 50mm separation?

Thanks

I'm not sure what the regulations say about mixing low and high voltage cable, that's not my field but..

I would avoid running them just inches apart. I'd be happier with them more like a meter apart (say next joist bay over) and even then avoid very long parallel runs.  If they must be run together go for CAT5 or 6 FTP which is a screened but quite a bit more expensive

To some extent it does depend on what you plan to send down the cable. Many people end up using their network cables for distributing analogue telephone, hifi or CCTV signals and they are more prone to interferrence than regular network traffic which has error correction upto a point.

Regs say min 50mm gap between band 1 and band 2 circuits, or all cables insulated to the highest rated cable in the bunch or if in trunking they should be separated by a barrier. Something along those lines anyway...

Somebody wearing a tie, thick glasses and a top pocket full of pens (who has never left the lab or worked in the real world) probably got paid a lot of money to figure that one out  

From an interference point of view running in the next compartment of a plastic trunking system is no different from running the same distance away with no barrier.

The rule in the regs is afaict more about preventing faults/damage from accidently putting mains onto ELV cables. It's probablly overkill with modern sheathed cables though (personally i'm surprised that you can't get cat5 with a mains rated sheath, it would seem very usefull for getting arround this).