Help/Advise needed - Need to modify existing extension

[wkpathan]

We have just purchased a house that has two extensions currently, with a total rear extension of 5.2m (<6m) from the rear wall of the dwelling house.
Now, we want to extend the width of the second rear extension to be in line with the width of the first rear extension, i.e. we want to move below marked wall (W1) to bring it in line with the kitchen side wall (W2).

1. Is it allowed without any planning approval?

2. Basis my research I think i need to apply for Prior Approval - Larger Home Extension.
But, when I tried to do so via Planning Portal, the site plan that I got shows our building as below, i.e. the two rear extensions are not shown correctly, in reality there are two steps in the width of the house while the site plan shows just one. Now I am confused about how I should show this change?
Can you please advise how I should proceed as I am showing the actual planned change versus what the site plan of the planning portal allows me to do? Do I need to change the site - if so, how to do that?

Thanks in advance!

 

[^woody^]

OS maps may not be accurate, but the site and location plans you submit as part of an application must be.

You need to edit the plan in any way you are able to show the existing and the proposed new. Download the plan and edit it outside of the planning portal if it can't be edited online

Be sure that when you edit the plan that your edit does in fact match the existing arrangement for the corrected layout, and the edit does not look like proposed work.

The alternative is the annotate the drawing with text to describe the incorrect layout

BTW, are you sure that this can be made via a prior approval application? It's not a large extension.