Firstly I will mention that there is no legal convention that property on one side owns one boundary in the property on the other side owns another. There is also no legal convention that the property that has the “good side” of the fence is the owner or vice versa.
Fences and boundary walls can be in 3 positions.
You need to remember that the boundary is a mythical pencil line on the ground.
So the boundary feature (wall or fence) can straddle the boundary line or can be all on your side oral on the neighbour’s side.
If it is all on the neighbour’s side you cannot touch it and vice versa.
If on the other hand it straddles the boundary both of you can attach things to it but neither of you can demolish it without the consent of the other. Nor could it be rebuilt without the consent of the other.
The reason for this is that anything which is attached to the land becomes part of the land. Therefore anything which straddles the mythical boundary pencil line is half owned by one property and half owned by the other and it’s impossible to separate the two.
It actually doesn’t matter who put the boundary feature up, the half which is on the neighbour’s land becomes the neighbours.
Even if there are T marks on the title deeds denoting responsibility for a boundary feature, that only applies at the date the deeds were drawn, things can change later. Although the marks may impart responsibility, it doesn’t put a liability to keep the boundary feature in good repair unless there is a separate covenant stating so.
So in your case, it really depends whether that 10 inches of land belongs to you or the neighbour because it belongs to the neighbour you cannot do it.
You are entitled to have reasonable access under the Neighbouring Land Act for any work required to maintain/preserve your property.
The Ivy is common-law nuisance because it is literally, on an English dictionary interpretation of the word, nuisance.
If it causes problems then you have a claim against the neighbour in negligence.
It will help if I explain how claims in negligence arise.
There needs to be
1. a duty of care
2. the duty of care needs to be breached
3. as a result of the breach there needs to be loss or injury
4. the loss or injury must be as a result of the breach
5. the loss or injury resulting from the breach must be reasonably foreseeable.
In order for there to be a claim in negligence, all 5 heads have to be satisfied.
Dropping the plumbline from the gutter is a good idea provided it’s accepted that that is where the boundary is because it’s not unknown for the boundary to be the wall and for the gutters and eaves to be trespass/encroachment. If your house has been there for a long time, then it is quite possible that the boundary is the edge of the gutter although if the neighbour doesn’t accept it, you are going to end up in the land tribunal with an argument.
You could get a boundary surveyor to given opinion. That’s likely to cost about GBP800 plus VAT. However you would both need to agree to be bound by the opinion otherwise, it isn’t actually worthless, but it would be good evidence for a land tribunal claim to establish actually where the boundary is.
Apart from the nuisance and negligence issue, this is really a boundary dispute over where the boundary should actually be.
Can I clarify anything else for you?
Please note that my answer is based strictly on the information that you have given me. If you have not given me all the information, then my answer may be incomplete or wrong.
I am happy to answer any specific points arising from this.
If you still need any points clarifying, I will be happy to reply because the thread does not close.