Light switch wiring query

[nae_mair]

hi. I went to put a new light switch in my porch that controls the light in there and the front door security light and when I took the old switch off the wall I found what you can see on the picture attached. Can someone explain why it is wired up like this?

 

[JAWS]

Borrowed neutrals is something different. This was common practice in the 70s to take the line supply from one level with the neutrals from another for two way lighting.

Thanks

 

[ipf]

Is it the term they use for borrowed neutrals

As well as the two way concern, in a case of properties, many borrowed neutrals occurred when the original CU had only one lighting circuit. A new mcb CU and the circuit being split into two, upstairs and down, resulting in a common neutral. Just bad practice.