1. You can remove anything which is on your side of the boundary and place it on your neighbour's side of the fence. Whilst the piece of concrete is your neighbour's property and should be returned to them, you have the right to remove anything on your side of the midpoint line of the boundary. The law gives a self-help remedy here. So, if you want, you can simply push the piece of concrete until it is no longer on your side of the boundary. There is no need to consult with your neighbours on this point. YOu simply remove it and place it back on their side of the midpoint line of the boundary.
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