Party Fence - Changing one side (Hit and Miss)

[Deleted User]

Hello, 
I have a hit and miss fence separating the rear of my property and "managed land" that's the responsibility of the builder/management agent for our development. 
The fence is new (2.5 years old) but is not straight (horizontally) and as it is hit and miss is letting all the weeds through from the unkept side of the fence. recently the developer has butchered the hedges that were providing cover between our garden and a new development (they were tall lovely trees with lots of cover) and we are now pretty exposed to the other houses.

We would like to replace our side of the fence (note below) but we aren't sure where we stand, we have been told it is a party fence and when we have previously broached the developer (who we are in ongoing litigation with for over year) they have refused to engage and just said no. 

Fence construction is the same as that shown here we would like to remove our side of the fence (just the vertical slats and put either featheredge or something similar to tie it in with the fence line on both the left and right side of our garden. We would also make it straight like this;

eddddy

'Party fence' usually means both neighbours are jointly responsible for maintaining the fence.
It's also possible that the fence belongs to your neighbour (the developer).

Either way, you can construct a fence on your own land (i.e. maybe a few centimetres in on your side of the boundary), which could hide the existing fence.  But if the original fence is a party fence, you might have a duty to maintain your side of it, so maybe your new fence could have removable panels for access, or similar.