Garden Wall height

[unclebob1]

I appreciate this may have been done to death - nearly- but I just wanted to check before I go ahead..

I have a garden fence at present which is no longer standing due to Wind.
In place of the fence I will be replacing it with a wall.

Now the side where the wall will be going is the boundary between my property and a PRIVATE alley way. Its not public, highway, neighbour etc.

The ground at the front of the house is approx 1m + higher then the ground at the back.
The ground in the alley way is approx 30-50cm lower then in my garden.

So:
1) is it still only 2m high that I can have the wall?
2) where is the 2m from? inside(which is probably built up), outside?
and the smaller gap between the ground and wall or the highest point?

 

[^woody^]

In terms of planning regulations it's 2m and measured from the higher adjacent ground level for each individual section

But if there is a 1m difference in height, then building a wall higher than 2m needs a bit of thought, if you don't want it to go the same way as the fence

 

[unclebob1]

Thanks woody,

To clarify, the garden slopes down from front to rear by approx 1 meter over approx 30m length.
I'm looking to have each 3m section stepped to keep it approx 2m following the ground, - the intention will be in the future to have both sides roughly the same by reducing the height in the garden side to the "natural" ground level which I take as the alley (as i had to do for a PD 6m extension).