Thanks for the reply. My diagram is incomplete (and as I mentioned, pretty crappy). What I left off was the LED Driver wiring to the LED circuit. I left the Red and Black DC + and - wires there to show what I'd be doing. I am going to be running them all in series. So three channels (with 12 LEDs each) wired in series.
The only thing that's wired in parallel is the LED Drivers but they have mechanisms to deal with this (they have fuses etc.) so there's really not an issue with this diagram.
The problem you mention, I have encountered discussions on it before. There's an issue when you wire in LEDs from 1 power source in parallel. If one LED blows then that parallel portion gets increased voltage / current and this can overheat and cause great issue with the LEDs and surrounds. However my LEDs are just a string of lights in series together wired to an individual driver.
I've already wired up my LEDs and tested them a while ago and they work fine. I only powered one LED Driver direct from mains power and I then swapped to the other channels. It's more just the isolation circuit (switch) that I was interested in. Since AC alternates I was wondering whether knocking out one half of it (via the SPST switch on the Live circuit) would "shut down" the circuit or whether you need to close both sides (SPDT switch on Neutral and Live) to fully close it.