I got the cable tray accessory when I bought the desk, and it's OK. The one thing that it doesn't cope very well with is power strips. If you put the strip on the tray, it becomes very difficult to plug-in/remove anything larger than a standard UK plug (think wall-wart plugs here). It's also a bit of a PITA to fit.

I'm thinking that the correct answer is a couple of L-brackets, some Contiboard mounted vertically -- like a fairly short privacy panel, and then to mount the power strips (and some sticky cable tidies) to that.

(*) I'm re-examining the desk arrangement because I'll be mostly WFH as of Monday, so I needed to tidy up my study.