On some of the more cheap n' nasty brands of dado, Simon, the boxes are not so much boxes as 'frames' so the mains sockets are open to the compartment behind.
Yeah, I've come across that. This was (IIRC) Rehau stuff, so I suspect vey much not cheap.
For good measure, the first thing I considered was adding an extra divider to give a second side compartment. The stuff they used came with one big section including the socket boxes and the lower "bevelled" area, plus an upper "bevelled" area with separator moulded into the base - so the top section had a clip on lid, but the bottom section lid was part of the back. The sparky told me that no such thing was available - I didn't have internet at the time (the joys of working in a Cumbrian seaside town), but when I got back to the office I checked - and sure enough, there's a separator available to turn it into 3 compartment trunking.
I see the flip side of your point quite often as well, We put in a load of new circuits and run a basket for them, then the IT department arrive... data cables on the power basket, data cables lashed across the ceiling grid, data cables tucked behind my conduit saddles to a workbench with a piece of IT equipment on it and the end just crimped in a 8p8c. And that's not including the ones who try and add their own fused spurs and sockets!
I didn't know you'd seen any of my work
Yes, there's cowboys on both sides, and to be fair, there's plenty of my cables run along ceiling grids. I do normally drop mini trunking down and put sockets on though. Sometimes it comes down to what the customer is prepared to pay for.
One job, I arrived with a cabinet and patch panel, to be told in no uncertain terms that the customer wasn't wasting money on stuff like that. So he ended up with a switch crewed to the wall and loads of cables with plugs crimped on. Thankfully they are no longer a customer - the sort that (sometimes) ask for advice, then completely ignore it, and when the lashed together network falls over (again) tries to make it your fault
How sad we were (not) to see the <expletive redacted> in court getting found guilty on H&S charges (death of an employee) - and that's apart from his public tantrums when the planning committee threatened to withdraw his site licence because he had refused to comply with public safety improvement notices (we could just hear him shouting "I'm not paying that" whenever anyone quoted for the work).