I live in an area where boundary encroachment appears, on the prima facie evidence, to be accepted by the region's planning authority, i.e. it appears to be 'the norm'.
Three instances involving detached properties come to mind. My son-in-law's detached garage was built with the wall at his neighbours side a wall thicknees over the percieved boundary (on his neighbour's side) line: the drain was clearly aon his neighbour's propety! Neither my son-in-law or the neighbour or either of their solicitors challenged this! I still wonder why to this day.
As it had a pitched roof the eaves and guttering must have projected another foot at least into his neighbour's 'airspace' yet the planning department seemed to be "perfectly O.K. with this since no one from the planning department, clearly, had challenged it - turning a blind eye more than a probability.
In my own case I'd "O.K'd" the line my neigbour took when setting out his detached 20'x12' - setback to end of garden - garage, i.e. the wall was "exactly" (for all intents and purposes) on the common boundary. I had not long moved in as second owner of my house; he had been in his from new and had long since submitted plans for approval for the garage before I arrived; consequently I didn't have sight or warning of his intentions and, in absence of any contrary searches unearthed by my solicitors there was nothing in this respect to draw to my attention - that's if he checked of course :=D.
What I hadn't taken into account, but I'm sure my neighbour had, was the eaves overhang and guttering once the roof was on. Indeed when it eventually was installed a few months later the eaves plus guttering overhang was around 14 inches plus the fact the water collection pipe ran the whole 20' length of the garage and was hanging on my side of the boundary enforcing on me an implied responsibiltiy to ensure I occasioned no damage to it accidentally or carelessly. The rub was that he also requested future access to the rendered wall for peiodic maintenance for painting and weather sealing. Furthermore, I soon realised that because of this and the significant overhang I was prevented forever from building up to the boundary in a like manner: he had been first to stake his claim to the boundary line and I ,essentially, was expected either to like it or lump it. Soon after the garage was finished with overhanging eaves and guttering I was offered a 5 year contract to work in Europe which saw me neatly into my retirement year. On my return we decided to move house. For the record the neighbour on my other side had done exactly the same thing, but it was a fait accompli before I moved in. Again I was denied the freedom of developing my property up tho the boundary and yet both my solicitors and the planning authorities saw fit to ignore it. If the wall was at the boundary where were the foundations.......? Is there no code of practice or regulation to prevent boundary encroachment, actual or implied, of this kind?