Wiring – have 4 brown (live wires) in the light switch – and no blue (neutral)

The cable on the left runs to the switch. Power comes in from one of the two other cables via red, runs down the red of the switch cable to the switch. When the switch is closed, power runs back along the black and into the light via the brown. Goes thru the lamp into the blue, which connects to the common neutral black of the other two cables.

Switch legs can be confusing because the neutral coloured wire carries power back the the switched fixture. All is as it should be though.

You have some pretty weird wiring to the light fitting. It looks like at the light fitting (fed from top-right romex at box) you would find

• the "ground" wire (green or bare copper in the US?) is being used as a neutral return from the light bulb.
• the "hot" (black) is a switched hot to the light bulb.
• the "neutral wire (white) is being used as a permanent hot for some other purpose.

So I'd expect an ordinary light fitting to be using the false "ground" and switched hot wires only.

The permanent hot (false neutral, white) might have been used (now or previously) to power some kind of device that needs live power. For example a remote light control or a ceiling fan that is operated by a pull-cord independently of the light bulb itself.

I would check the wiring in the light fitting controlled by that switch. Then I'd label the wires at each end to make clear what each wire is really used for. Alternatively, you could rewire it properly - that would be best if the light fitting is a normal conventional simple light only. I'd double check that something else (an extra outlet?) isn't already wired from the light fitting end - disconnect the white wire from the three black and see if an outlet or something stops working.

If you can't figure it out it might be best to call an electrician.