The Buried Threat: Why Mine Shafts Matter in Conveyancing

It’s just a single line in the form, but it can influence lender appetite, insurance, buyer confidence, and price.
In this bite-size read, we separate perceived risk from actual risk and outline the steps that keep transactions moving.

The national coal mining database holds records for over one hundred seventy thousand mine entries in Great Britain. Not all have the same evidential detail, and some historic entries are unrecorded. In fact, a general rule of thumb is that for every one recorded mine entry, there are two more unrecorded within 50 metres. That’s why interpretation matters.

Within the Coal Authority’s database, records can include whether the feature is a vertical shaft or horizontal adit, its diameter, depth, treatment history, and other attributes. These fields form the backbone for interpreting mechanism and consequence, rather than relying on simple distance rules.

Perceived risk is the reaction to seeing a shaft symbol near a boundary line. For some buyers, that perception alone is a deal breaker. Even if one buyer is comfortable today, a later buyer may not be, which affects resale confidence.

Actual risk depends on mechanism for potential collapse or subsidence. That means depth, geometry, ground conditions, treatment history, and whether the feature lies beneath or beside the structure.

A nearby adit that heads away from the plot may present negligible risk despite proximity, while an untreated vertical shaft beneath a boundary wall is a genuine hazard. The so-called Zone of Influence varies with site conditions, so distance alone rarely tells the story.

Prospective purchasers — Risk appetite varies. Some will accept a clearly explained low-risk position if treatment is documented. Others will walk away on principle.

Lenders — Many high street lenders default to caution where mine entries are close to or beneath structures. They’ll want an official CON29M and, where flagged, further interpretation (unless it’s included in the CON29M).

Policies differ, but lenders may reduce loan-to-value, request investigation, or decline if clarity is lacking.

There’s no single official discount figure for mine entries across the UK. Impacts are case-specific and depend on feature type, position, evidence, and local market sentiment. Public valuation standards emphasise evidence-based judgement rather than a flat percentage.

Still, let’s look at a real example.

The Bickleys bought their home in the mid-2000s. At purchase and remortgage, no mine entry appeared nearby.

In 2014, when selling for £240,000, a new mine entry appeared on the CON29M within 5 metres of the back wall. It had been added after an old map was digitised.

There was minimal data, just a point on a map. Years later, interpretation showed it was a shallow prospect pit, later confirmed by sonar investigations.

But the perception alone killed multiple sales. The property eventually sold for £180,000, a £60,000 reduction, wiping out their renovation value.

This is one of many examples showing how perception alone can affect saleability, even without physical risk.

1. Mine entry 20–5 metres from the boundary
Aim: Confirm mechanism and likelihood of influence on the structure.
Typical action: Level 3 Building Survey noting any movement, with a watching brief for future signs.
If movement is evident, notify the Coal Authority under their duty to investigate subsidence.

2. Mine entry within 5 metres of the structure (not beneath)
Aim: Reduce uncertainty through qualified mining engineer inspection and desktop assessment using planning, borehole, and construction records.
Why it matters: These can show whether the entry was a modern access shaft or an adit heading away — both can reduce perceived risk.

3. Mine entry beneath the property
Reality: A genuine risk to enjoyment, value, and saleability. Expect investigation and potentially engineered treatment or capping.

• Permitting costs: Around £4200 per shaft or adit (permit charges only).
• Investigation cost: Typically £5–15,000 depending on access and probing.
• Treatment and capping:  Highly variable; can exceed tens of thousands for reinforced concrete caps or drill-and-grout stabilisation.

This is the gap Martello set out to close.

A mining search shouldn’t stop at saying a feature exists. It should explain, clearly and in plain English, how that feature affects the site and what to do next.

In the Martello Official CON29M, we evaluate, display, and interpret Coal Authority records to explain the practical consequence and recommended next step. Where a mine entry lies immediately adjacent or beneath a property, an expert reviews the context to give clearer, decision-ready actions.

The result, a report you can lift straight into client and lender conversations without another round of clarification.

Saving time, money, and stress.