Tree safety inspections: a UK practitioner's guide

No UK statute requires trees to be inspected on a set schedule. The obligation is indirect, and comes from three places at once: the common law of negligence, the Occupiers' Liability Acts 1957 and 1984, and — where employees or the public are affected by work activity — the Health and Safety at Work etc. Act 1974.

The practical test courts apply is reasonableness. A duty holder is not expected to eliminate risk from trees, which would be impossible; they are expected to have a proportionate system for identifying foreseeable risk and acting on it. The National Tree Safety Group's guidance Common Sense Risk Management of Trees remains the reference point most UK practitioners and insurers work from.

This matters for how you record work. When a tree fails, the question is never "was the tree safe?" — it is "what system did you have, and can you evidence that it was followed?"

Proportionate management starts by dividing the estate by how many people are exposed to it and for how long. A typical zoning model looks like this:

• Zone 1 — high occupancy: carriageways, footways, school grounds, car parks, play areas. Individual trees are recorded and inspected on a short cycle.
• Zone 2 — moderate occupancy: park interiors, minor paths, amenity grassland. Individual recording, longer cycle.
• Zone 3 — low occupancy: woodland interiors, land with no formal access. Often managed by zone-level walkover rather than individual tree records.
• Trigger-based inspection: after storms, after adjacent works, or when a defect is reported — regardless of zone.

Zoning is the single decision that determines whether a programme is affordable. On a highways network, treating every tree as Zone 1 produces a survey burden nobody can fund; failing to identify true Zone 1 assets produces liability nobody can defend.

Frequency follows the zone, not the calendar. In UK practice, Zone 1 assets are commonly inspected annually or biennially, Zone 2 on a three-to-five-year cycle, and Zone 3 by periodic walkover. Species and condition shift this: ash affected by ash dieback deteriorates fast enough that a tree recorded as Class 2 one summer may be Class 3 or 4 the next, so ADB-affected stock is often re-inspected inside twelve months.

Whatever cycle you set, write it down and apply it. A documented policy inconsistently applied is worse evidentially than a modest policy applied properly.

The record is the deliverable. An inspection that happened but cannot be evidenced is, for practical purposes, an inspection that did not happen. Each record should carry:

• A stable unique reference for the tree that survives across survey rounds and contractors.
• An accurate location — coordinates, not a description. Reconciling 'third oak past the gate' between two contractors is where most datasets fall apart.
• Species, approximate height, DBH and crown spread.
• Physiological and structural condition, recorded against a consistent scale.
• Identified defects and the target they threaten — the target is what makes a defect a risk.
• The recommended work, its priority, and a target completion timescale.
• Dated photographs tied to that inspection, not to the tree generally.
• Who inspected it, their qualification, and the date and time.

The last two items are the ones most often missing, and the two that matter most when a claim arrives.

Most organisations we speak to do inspect their trees. What they cannot do is produce the history of a single tree on demand. The survey sat in a spreadsheet, the photographs sat on a phone, the GIS layer was updated separately, and the following year a different contractor used a different reference scheme.

The fix is structural rather than procedural: hold the asset, its geometry, every inspection against it and every photograph in one record, so that the history is a property of the tree rather than something reconstructed from archived files.

That is the problem Arbrium was built to solve — inside a live national infrastructure vegetation programme, alongside the surveyors doing the work. You can see how that played out in our National Highways ash dieback case study.