Thank you for your question. My name is ***** ***** I will try to help with this.
What problems has this caused?
What problems would it cause if you did the same?
Alleyways like this between two terraced properties are rarely jointly owned. There are potentially several ways that they can be owned.
One property can own alleyway and the other one can have access over it..
Each property on either side and owns to the centreline and each property then has the right to go the other persons side.
The division can be the other way round whereby one property owns the front part of the alleyway and the other property owns the back part of the alleyway and each has the right to go over the other persons part.
It would be necessary to look at your deeds to see which is the case.
If he has built on your land with these blocks than it is trespass and you can take action to get trespass removed although the court may not do that if these have been in place for some considerable time and you have ignored them or you did not raise the issue with him while he was doing it. In the latter case the court would award you compensation rather than asking to remove the blocks this access severely restricted which I will now tell you about.
If he has narrowed the width of the alleyway to make it so tight that you could not (for example) get a wheelbarrow in and out then he also obstructs your right-of-way. The legal test for pedestrian access is, surprising though it may seem, whether you can take a wheelbarrow in and out. Before right-of-way is said to be obstructed the obstruction must be substantial. There is however no definition of substantial and each case would be looked at on its own facts.
It would come down to whether you could still freely walk up and down the alleyway this narrowed it substantially.
Can I clarify anything for you?