Water leak in terraced house

[Super111]

I’m posting under a different name for privacy reasons.
I would be grateful for any suggestions on what I should do next and where I stand with this.

About three weeks ago, I noticed a small water stain appearing on the living room wall downstairs. I have attached a picture taken a week ago for reference. At first it was quite faint, but over time it has gradually grown and is now spreading along the junction between the wall and the ceiling. The area feels slightly damp to the touch.

I live in a terraced house. The room above the affected area is a child’s bedroom, and the bathroom in my property is on the opposite side of the house. However, the stain is exactly on the shared wall with my neighbour’s upstairs bathroom. My neighbour had their bathtub, toilet and sink fitted about two years ago.

I initially spoke to the tenants next door, and they said there was no water pooling or visible leaks in their bathroom. Even so, they arranged for the company that installed their bathroom to come and inspect it. The tenants usually deal with most repairs themselves, as they are concerned about their rent going up, so they asked me not to contact the landlord directly. I agreed to wait for their plumber to come and inspect the issue first. When they came, they didn’t open up the wall but removed the bath panel and concluded there was no leak in their installation. They suggested instead that the issue was coming from my property.
For context, there is also staining on the wall in my neighbour’s downstairs toilet area.

Because the damp started developing mould in my property, I contacted my insurance company, and today they sent out a plumber they work with to investigate. He found that there are no water pipes running through the party wall in question, my bathroom is not located above the affected room, and my roof was completely replaced last year so there is no possibility of a roof leak either. His conclusion was that the leak is not coming from my property at all. If it were, they would have started opening up my wall today to investigate further, but he ruled that out entirely.

The problem is that the mould is getting worse, and I want to resolve this quickly. However, the neighbour’s bathroom installers have already suggested it is coming from my side, and I suspect both the tenants and the landlord next door may believe that.

My insurer’s plumber has basically said there is no plumbing on my side that could be responsible, so it must be coming from the neighbouring property, but beyond that there’s not much more they can do. I dropped a letter to their landlord today as they weren’t in at the time.

I’m now unsure how to proceed if the landlord is not willing to engage with the issue. What would be the best next step in this situation?

@askmenow We have been paying a management company appointed by the landlord for several years, as we assumed these payments were required. One of the other homeowners contacted a solicitor to clarify whether these payments were necessary, and was advised that he should continue paying or risk losing his property.

It is rather amusing that when the landlord was not charging us, everything was managed quite efficiently. However, as soon as charges were introduced, the quality of service has become quite poor. You would expect it to be the other way round.

I don’t believe any agents are involved with the property next door. We have never seen their landlord since we purchased our house in 2018; the tenant moved in shortly before we did.

@JohnofWessex Sorry I wasn’t able to update you earlier — I’ve been rather busy.
We haven’t contacted the council yet. Following the surveyor’s advice, the next step is to have a plumber we trust come round this Friday. He will either open up the affected wall or lift the floorboards upstairs to properly check that the issue isn’t coming from outside.
We’ve already spoken to the insurance company to confirm that we can go ahead, and they’ve said they will cover the cost of the work carried out by this plumber.
If it turns out to be our responsibility, we’ll ask the plumber to fix the leak. If it appears to be coming from the neighbouring property, we’ll speak to the neighbour to see if they can provide their landlord’s details. If they’re unwilling to share this information, we’ll contact the council. If the council is unable to assist, we’ll then seek help from the legal team through our insurance company. Thanks.

I meant our side, not outside

Here’s a new update.

Our trusted plumber came round today and immediately said the only likely cause was next door. He cut a hole in the ceiling to investigate properly — and yes, it was the neighbours after all… The plumber wanted to inspect next door, so we went round and checked their bathroom. Turns out the bath hadn’t been sealed around the edges, and there was also water dripping from the pipework. Our plumber took photos and videos of everything.

I honestly don’t know what their plumbers did to conclude it was coming from our side. Our plumber found the leak within minutes without even needing to cut into their wall.
I do feel reassured now that we finally know the cause, but at the same time I’m furious — both with next door and with the plumbers who fitted their bathroom. We really didn’t need to go through all this hassle.
My husband suggested they use our plumber to sort the problem, but they seemed hesitant about it. We’ll be submitting a full report to our insurance company once we receive all the photos, videos and evidence from our plumber.

If they dont sort it then either your insurers can take action or The Council can serve notices and/or do the work in default