wall is 'our demise'

[JustAnotherOpinion21]

Hi everyone, just wondering if anyone can offer and explanation or any similar experience...
We bought a 2 bed house - shared ownership. We've come into money, so are able to staircase to 100% which in turn becomes a freehold property.

We were thinking of adding a conservatory extension in the back garden, which would mean moving the garden gate further along the garden wall.

Our housing association has told us that the garden wall we would need to alter, is 'our demise' and I'm not too sure what this means!
Just to add, the garden wall separates the front and back gardens. The back garden is ours, and the front garden is the housing associations. When we staircase to freehold 100%, the garden is still the housing associations.
I've tried to google results and that was confusing and unhelpful!

What does our demise mean when referring to a wall and do we really need to ask permission to make changes to it if it's ours?

Sorry if that doesn't make sense!

freeconveyancingadvice.co.uk/Q&A/landlord-leases/garden-not-mentioned-in-demise

it means the wall belongs to them.
drawing would help, can you locate the gate elsewhere.
remember, any improvement you do, must be mentioned to them otherwise when it comes to staircasing they will share the value of the improvement with you.
or do your final staircasing, pretty simple(in case you have the fund) or request advance from your lender.
then, do proceed with improvement( yours 100%)
I hope it makes sense.

Thanks @pinkshrimp & @mumsy27

Have attached a layout of the property. The wall with the T against it is the wall I'm talking about. At the moment the garden gate is next to the house at the end of the front garden path. We would like it moving to where the bright green line is.

If we move it, we can have our conservatory against the wall. If we cannot move the gate to where we would like, we would either have to build up against the gate&wall rendering it useless, or have a smaller conservatory with a small pathway between the wall and conservatory - ultimately a waste of space!

The HA said it doesn't think it would be a problem, just the amount they're asking for for us to submit the request, then the amount for their surveyor etc is mad. I was thinking if the wall was ours, we'd have more control... I've emailed to ask them, they're just so slow with replies!

Your demise is your area of ownership / responsibility

The T also indicates it’s your boundary