Apologies for the recent noise, the mods seem to have silenced it for now...
The neutral, should correctly be sourced, if it has been installed properly, from the very same source and MCB, as the one which supplies the light. Which means it should be connected to the neutral, of your cellar circuit. If it is (wrongly) connected to the neutral, borrowed from a different circuit, then it is called a borrowed neutral.
The borrowed neutral, if it is borrowed, would not be obvious at the moment, due to all your circuits appearing to be fed from a single RCD, and individual MCB's. If in the future, the RCD + MCB's are upgraded to RCBO's, a combined RCD + MCB, one per circuit, then you will suffer tripping of the RCBO's, due to the borrowed neutral.
It obviously not connected to that socket, in the photo, but there is an issue with that socket - the amount of debris. The debris, might - I said might, cause a low value on an insulation test of the installation, should it become damp. Were it me, I would turn the power to the socket off, and see if I could clean it out with the hose of a vac., and maybe the use of a paint brush.