I have tried to draw a diagram to explain this, but I don't know if it will make sense!
I am buying an end terrace on a row of terraces that have steps up to the front door- down the side of my house is an alley for access to other houses gardens, these houses are at street level so are lower down than my house (see diagram). There is a house behind the street level house on this pic, also at street level.
As a result, my back garden overlooks a back garden of this house- you can literally look down into their garden and their living room etc. The garden currently has a short wall, however we will want to put in a higher fence for various reasons. I understand legally we can put a 6ft fence in, but could they take issue with this?
I would think from a privacy perspective it's better as we won't be able to peer in anymore (not that we would be peering anyway as a matter of course but it's almost impossible not to, you are literally on top of their garden)- but if it obstructs a view or sunlight, where would we stand legally?
Rubbish pic attached!