@Esther In which department is the property situated ? You never know, there might just be someone on this forum who is close by and who can help you out by visiting from time to time.
Also, when you said that your property is attached to the neighbours property, did you mean that the houses are attached to each other (semi-detached), or that your land and the neighbour’s land abut one another ?
Personally I think that trying to “get even” is a pathway to misery. Things will escalate and because they are there and OP is not then OP will come off worse.
Only concentrate on things that lead to selling the house. Everything else is secondary.
just stopping at “don’t get mad” is sufficient imo.
What you do beyond that (if anything) should not be apparent to the casual onlooker.
revenge is a dish best served cold 
great advice.
Thanks for the example you have submitted.
It just confirms what I was saying, despite of one could think by just reading the title in bold.
So much excellent advice here – thank you all.
The house is in Haute-Vienne, near Droux.
Based on your responses, I am currently considering the following course of action:
I will update here as to how events play out. I understand that I will have to declare this to any potential buyer but, as I previously mentioned, they’re going to know there’s an issue anyway when they ask the provenance of the huge pile of junk!
Again, really grateful for all your good advice.
Hi Robert, the houses are semi-detached, and the property is in department 87.
Hi Esther,
Thanks for the clarification.
A couple of points come to mind. You said that you inherited the property but you didn’t mention when that was, so I’m thinking that if it was a long time ago, maybe the neighbour is trying to claim ownership of the ‘abandoned’ land by making use of it for the purpose of ‘storage’ and the stabling and grazing of animals. In such a case it is imperative for you to be able to prove that you have challenged, and denied permission for, his ‘occupation’ and ‘use’ of your land.
You mentioned that the neighbour is interested in buying the land in question, so perhaps they are trying to ‘acquire’ it by less expensive means.
Should the matter need to be officially resolved, it will be necessary to be able to prove not only that you wrote to the neighbour to challenge, and deny, his occupation and use of your land, but also that he actually received the letter. Here in France this is done by sending the letter Recommandée avec Avis de Réception, and in this way you receive back a signed confirmation of delivery. I appreciate that this is probably impossible for you to do from the UK, but I am willing to do this for you from here in France on your behalf. I will take the liberty of sending you a PM (Private Message) on this point if you don’t mind.
Marking the boundary of your land is also extremely important. This does not need to be expensive as something as simple as a line of stakes, such as 4 foot lengths of steel reinforcing bar hammered into the ground, connected with a length of cord, chain, or thin rope would be sufficient. Just take a couple of photos of the boundary marker line in place for future reference. Turn on the camera time / date stamp feature, and place the front page of a newspaper for that day in one of the photos. If the marker line does end up ‘accidentally’ knocked down, that will not be as relevant as being able to prove that it was there in the first place.
I’m also wondering if you know what the situation was between the late owners of your property and the neighbours. Did they get along with each other, or was there always animosity between them. Perhaps there is some dispute of long ago that caused the present situation, and if so, then perhaps it might be possible to resolve that matter in order to alleviate the current tensions.
Things sent LRAR have been challenged in courts as they do not prove the contents of the letter. The people they are addressed to can also just not sign for them - and a certain type of people will never accept a LRAR as they know they are unlikely to contain anything to their benefit.
When dealing with giving notice to tenants we were strongly advised to use a huissier’s letter. More expensive of course, but more certain and can be organised ar a distance.
This sets out the difference
You can send an LRAR letter online via the La Poste website and this give you full tracking. I used this service around a year ago, and I just checked on my espace client and the letter I sent is archived in my purchase history. It can be downloaded to read the contents. I do not see how a court can argue with that.
Having said that I have also used a huisser, I cannot remember the cost but I do not recall it being outrageously expensive, and the process was very easy.
True there is a letter service, I forgot that. Can you modify the standard letters?
However still leaves the issue that the people concerned may not accept the letter. And the post person cannot force it on them, whereas a huissier can (well not force, bit insist with power of the role).
In a court case, the defendents lost out against me because they did not send letters by LRAR and the judge ruled them non-existant because of that fact. This was at TGI not a small local court.
I do not know about standard letters. The service i used, I simply typed out my own letter and submitted it via the online process, paid the fee and La Poste printed it off their end and delivered it LRAR. I found it an excellent service.
But you are right, it still depends on the person accepting the letter. You can track this so you will know immediately whether or not it has been accepted. I cannot remember the details but it is clearly explained, I believe La Poste makes at least two attempts to deliver it, though in my case this was not necessary.