A blocked drain in a Central London mansion block is rarely that simple, because the pipe that's actually full of water may not belong to you, may not belong to your freeholder, and may not even belong to your building. Before anyone reaches for a plunger or a phone, it's worth fifteen minutes working out which of those three it is — because that decision determines who pays, who you call, and how fast it gets sorted.
Start with where the blockage actually is
Every flat has its own branch pipework — the run from your sink, bath, shower or toilet to the point where it joins a shared stack or drain. If only your kitchen sink is backing up and nothing else in the flat or block is affected, the fault is almost certainly in your own branch or trap, and that's your repair to arrange and pay for, in the same way as any other fitting inside your demise.
If more than one flat is affected — your neighbour's toilet gurgling when you flush, or a smell rising from a shared gully at ground level — the blockage has moved past your pipework and into shared drainage: a soil stack serving several flats, or the underground drain run that carries waste from the building to the sewer. That's a different conversation, and it usually isn't yours to fund alone.
Whose responsibility is shared drainage?
This is genuinely lease-specific and there is no single rule that applies to every block. In most leasehold blocks, the pipework and fittings inside your own flat sit within your demise and are your responsibility, while shared stacks, risers and underground drains serving the building are typically part of the common parts that the freeholder or the residents' management company is responsible for maintaining — funded through the service charge. But "typically" is doing real work in that sentence: the actual boundary is set out in your specific lease, and it can vary between buildings, and even between flats in the same building if leases were granted at different times. Read the demise and repairing covenants before assuming either way, and if it's unclear, ask your managing agent to confirm it in writing rather than guessing under pressure with water on the floor.
Where a drain runs beyond your building and connects to the public sewer network, there's a further layer. Under the Water Industry Act 1991, as amended by the Water Industry (Schemes for Adoption of Private Sewers) Regulations 2011, most private sewers and lateral drains connecting properties to the public sewer network in England transferred into water company ownership on 1 October 2011. In practice, that means a blockage in the section of drain between your building and the public sewer may be your water company's responsibility to clear, not the freeholder's — worth checking before anyone commissions an expensive CCTV survey unnecessarily. Your water company can usually confirm whether a specific run has been adopted.
What actually happens when a shared drain blocks
- It's reported by whoever notices first — often a resident, sometimes a porter doing rounds. Get it to the managing agent immediately; shared drainage sitting for a weekend gets worse, not better.
- A plumber attends and locates it. Rodding from the nearest access point (an inspection chamber, often in a communal garden, basement or under a manhole cover) usually clears a straightforward blockage the same visit.
- If rodding doesn't clear it, a CCTV drain survey follows — a camera run through the pipe to find root ingress, a collapsed section, grease build-up, or a genuine structural fault. This is the point where cost and time both step up, and it's also the point where "whose pipe is it" gets checked properly, because a survey usually shows exactly where the run crosses into public sewer.
- Access and scheduling in a block is its own task. Getting into a communal chamber, coordinating a porter, or booking a working window that suits the building's rules takes planning — see our guide on porter access for mansion block works for how that usually runs.
When it's an emergency and when it isn't
A slow-draining sink is an inconvenience. A blocked drain that's backing up into a bathroom, overflowing an external gully near a front door, or causing sewage smell inside a flat is not something to leave until Monday. Foul water in a flat is a health and property risk, and it tends to escalate fast in occupied buildings where several households share the same run. Treat it the way you'd treat any water emergency: report it immediately, and if it's actively coming back into the property, call an emergency plumber rather than waiting for a scheduled visit. The same urgency applies to anything resembling a burst pipe in a mansion block — water and shared pipework in a block of flats is one of the few situations where speed genuinely limits the bill.
Cost and how it's usually split
A straightforward rodding job attended as a normal plumbing call-out (contact us for the current rate), which covers diagnosis and often the fix in one visit if it's a simple blockage. If the blockage sits in shared drainage that's the freeholder's responsibility, that cost is usually recharged through the service charge rather than billed to the individual flat that happened to report it — but confirm this with your managing agent before assuming, because some leases handle recharges differently, particularly where a specific flat caused the blockage (wipes, fat, or building debris flushed by one household are a common and entirely avoidable cause). If the drain turns out to need CCTV survey and repair work — root cutting, relining, or excavation — that's a larger job priced by quotation once the survey has identified the actual fault, and in a leasehold block it may fall under the consultation requirements described in our guide to Section 20 major works for leaseholders if the cost per leaseholder crosses the relevant threshold.
What to do right now if a drain has blocked
- Stop using the fitting that's backing up until it's cleared — every flush or drain-down adds more water to a pipe that's already full.
- Photograph what you're seeing — where it's backing up, any smell, any staining — the same way you would for any leak, before anyone forms an opinion.
- Check whether more than one flat is affected. If it's just you, it's likely your own branch pipework. If it's several flats, it's shared drainage and the managing agent needs to know today.
- Report it to the managing agent or freeholder in writing as well as by phone, so there's a dated record of when the issue started.
- If it's actively overflowing or you can smell sewage inside a flat, treat it as an emergency and call rather than email.
Most blocked drains are cleared in a single visit once the right pipe has been identified. The part that costs time and money is usually not the clearance itself — it's the argument over whose pipe it was, which is exactly why checking the lease and the drain's adoption status early, rather than after a costly survey, is worth the fifteen minutes. If you're not sure where a blockage sits or who's supposed to fix it, send us a photo and a brief description through our contact form and we'll help you work out what it is before you commit to a survey.