High garden

[luxardo]

I share a boundary fence with my neighbour but my property is about a metre higher than his even though they are adjacent. The land slopes and there is a retaining wall between the two gardens under the fence.
This means if I stand on the patio outside my door the fence is below head height on my side but considerably higher on their side.
Am I right in thinking I can build a wall (inside my own garden) 1.8m high from the level of my patio without planning position ?
The top of the wall will be about 3m from the level of their garden on their side but only 1.8m on my side due to the slope.
The top of the existing boundary fence is already about 2.5m from the level of their garden but only 1.3m on my side

[des8]

Ground level is defined in the planning legislation [Town and Country Planning (General Permitted Development) Order 1995 1(3)] as:
the level of the surface of the ground immediately adjacent to the building (or fence), or where the level of the surface of the ground is not uniform, the level of the highest part of the surface of the ground adjacent to it.
So measured from the surface of the highest piece of land adjacent to the fence line you can erect a fence of up to 2m in height (or 1m if adjacent to a highway used by vehicles).
The restrictions relate to fences, walls (including trellises), gates but not hedges.

You need to look at the natural height of the land which has probably been disturbed as there is a retaining wall.
Have you discussed the matter with your neighbour?
If there is likely to be a dispute consult your local authority planning department

[luxardo]

Thanks. I think I'm ok then as the wall is less than 2m in height from my patio paving (which is directly outside my patio doors).
A retaining wall runs the full length of the paths between our houses. If I'm on my path and he is on his path I'm a metre higher even though we are stood next to each other. This continues half way down the boundary fence at which point the land slopes off and both gardens are level at the bottom.
I should mention these are new build houses, only 2 years old.

[des8]

If new build check there are no covenants restricting height of fences

[luxardo]

There are none, I checked. Just something about both properties being jointly responsible for the boundary fence.

[des8]

If you propose to build the wall on your side of the boundary there should be no problems

[FergusonJes]

In my opinion, you have every right to build that wall, but for any eventuality, it would be good to still turn to an expert in the field who will tell you everything with precision.
Personally, I also have a large garden that I love to take care of and always renew, but the problem is that directly at the end of it, the neighbor's property starts, but he doesn't want us to put up a fence.
By the way, if you need any ideas on this topic, I can recommend you to go on https://gardeningtoolshq.com because I personally took a lot of useful things and information from here.