I must admit that I saw that as essentially 3 walls, One with the red socket on it, one with the blue socket on it and the third on the short wall between them because it steps the other two back "dog legged" fashion, this short wall joining to and at 90 degrees to to other two would have been the one in question as to whether it is exceeding 300m and has any points on it.
Therefore is it a short wall forming an external corner to the LH wall (Blue socket) and an internal corner to the RH wall (Red socket) if more than 300mm there is no zone joining the corners unless it has a point there to identify a zone.
Although I think most would suspect cables might be present below finish wall level, it was not actually a zone.
Now we`ve seen the pic it does clarify a bit, before the pic we could only go off the drawing.
I think that some of us, because of trades working, have seen walls in all sorts of fashions, some you`d never expect in a million years unlessyou`d been in enough properties.
One funny instance, a few years back, I drilled a small hall in the internal corner of someone's kitchen gable end in order to get a bonding cable thru to the outside WC, I looked thru my hole and the décor colour was different. Then I checked the WC (the outbuilding, not the toilet itself) , no hole! Where the heck had my drill come out? The chap next door then came complaining I had drilled thru into his WC . I looked, yes a tiny hole into his outside WC, I offered to fill it in and he started on about a full paint job etc etc. For goodness sake it`s only a tiny hole in an outside WC wall in an old terraced house, not particularly modern or well painted and it was worn. Our customer said "Oh him, he whinges and moans all day everyday, good job I didn`t insist he remove his WC wall from over my side of the boundary a few years back.
The builder checked it all out and told our customer "Yes he has built his wall far over to your side of the boundary, I`ll go and offer a price to drop his WC wall and rebuild over to his side of the boundary",
The moaner heard this and retorted "Its only 7 and a half inches"" to which our customer replied "Not it is over a foot and I knew that when you did it but it did not bother me enough to moan about it but now you are creating a scene about a very tiny hole in an outside WC that you rarely use!".
He did accept a bit of filler but still continued to moan about the noise of building works because in his opinion we should wait a few years till they move out and do that noisy building works " we had kept noise to a minimum and within a 8:30 to 4:30 weekdays but he was constantly moaning right from the word go "Why does he want his house rewiring? It`s been OK for all these years!" etc etc.