Knotweed Next Door: how close are historical records to where people live?

We analysed 7,352 qualifying recorded-location clusters across Great Britain. More than half were inside or within 100 metres of a built-up area.

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THE NATIONAL PICTURE

Recorded knotweed often sits close to built-up areas

Of 7,352 qualifying historical locations studied across Great Britain, 3,981 were inside or within 100 metres of a mapped built-up area.

54.1%
inside or within 100m3,981 of 7,352 qualifying recorded locations
100m is used to describe proximity to a mapped settlement boundary. It is not a biological spread distance, risk zone or property threshold.
i

What the figures mean: they describe the selected historical records, not the share of British knotweed near homes. They do not confirm that knotweed is still present or that any individual property is affected.

THE GEOGRAPHY

What is a built-up area?

The study uses the Office for National Statistics Built Up Areas (December 2022), Great Britain boundaries, derived from Ordnance Survey Open Built Up Areas.

These 25-metre grid-based boundaries describe mapped settlement extents of at least 20 hectares. They can include buildings, roads, gardens, made surfaces and some non-built land.

They are not maps of individual homes, residential plots or land ownership. Small settlements and isolated rural homes may sit outside the mapped geography.

Distance is measured to the settlement boundary

Each location is measured by straight-line distance from its representative centre to the nearest mapped built-up-area edge. It is not measured to the nearest house.

WHY “NEXT DOOR” MATTERS

The practical issue can begin beyond your boundary

Knotweed on neighbouring or adjoining land can be harder to investigate and manage because access, responsibility and treatment may involve more than one landowner.

01

First identify it correctly

Many plants are mistaken for Japanese knotweed. Clear photographs and specialist identification should come before assumptions about liability or treatment.

02

Establish who controls the land

The relevant party may be a neighbour, council, railway operator, waterway manager or other landowner. Do not enter or treat land without permission.

03

Coordinate the response

A shared inspection, treatment plan and record of monitoring can be more useful than isolated action where suspected growth crosses or approaches a boundary.

RICS identifies lack of control over treatment on adjoining land as a particular practical difficulty. It also notes that serious structural damage to substantial buildings is uncommon.

DESCRIPTIVE LOCAL EXAMPLES

Three places that passed the publication checks

These examples are shown alphabetically. They are not a league table and should not be compared as a measure of local prevalence because recording coverage and provider activity differ between places.

Bridgend2016–2025
47 of 94

inside or within 100m

50.0% of the qualifying historical locations were inside or within 100 metres of a built-up area. Nineteen were inside the mapped boundary.

Principal sources: South East Wales Biodiversity Records Centre and Botanical Society of Britain and Ireland.
Liverpool2016–2025
69 of 71

inside or within 100m

97.2% of the qualifying historical locations were inside or within 100 metres of a built-up area. Of these, 58 were inside the mapped boundary.

Principal sources: Botanical Society of Britain and Ireland and Merseyside BioBank.
Shropshire2016–2025
31 of 73

inside or within 100m

42.5% of the qualifying historical locations were inside or within 100 metres of a built-up area. Thirteen were inside the mapped boundary.

Principal sources: Botanical Society of Britain and Ireland, Shropshire Ecological Data Network and the Environment Agency.
Why only selected local figures are shown

Each displayed 100m percentage is based on at least 50 cleaned locations and passed provider-removal and coordinate-uncertainty checks. Areas that did not pass every check are not given a headline percentage.

PRACTICAL GUIDANCE

What to do if you suspect knotweed nearby

A historic record is context, not a diagnosis. If you are concerned about growth on your property or adjoining land, focus on current evidence and proportionate next steps.

Learn how to identify Japanese knotweed →
  1. 1
    Do not disturb the plant

    Avoid cutting, digging or moving soil until it has been identified.

  2. 2
    Take clear, dated photographs

    Capture stems, leaves and the wider location without entering somebody else’s land.

  3. 3
    Arrange reliable identification

    A specialist can assess the plant, its location and whether further investigation is needed.

  4. 4
    Speak to the relevant landowner

    If growth appears to be beyond your boundary, establish who manages the land and discuss coordinated access and treatment.

  5. 5
    Keep a written record

    Retain photographs, correspondence, survey findings and treatment documents, especially before a sale or building work.

HOW THE STUDY WAS BUILT

Methodology in brief

The analysis turns individual source observations into a more conservative set of recorded-location clusters, then measures their proximity to a fixed settlement geography.

From source records to proximity findings

019,536qualifying source-observation centres
027,352cleaned location clusters
035cumulative distance bands

Each cluster is counted once in every cumulative threshold it meets.

01

Source and period

NBN Atlas Japanese knotweed records dated 2016–2025 across Great Britain.

02

Qualifying checks

Records were filtered for commercial licensing, accepted identification, usable dates and coordinate accuracy.

03

Cleaning and grouping

Nearby observations were grouped to reduce repeat counting of the same recorded place, producing 7,352 clusters.

04

Proximity calculation

Straight-line distance was calculated from each representative cluster centre to the nearest December 2022 built-up-area boundary.

Important limitations

Historical, not current. A record may relate to knotweed that has since been treated or removed.

Recording is incomplete. Low or zero counts do not prove that knotweed is absent.

Provider activity varies. Some areas have been surveyed more intensively than others, so no local rankings are produced.

Coordinates vary in precision. The cleaning rules reduce this problem but do not turn observations into property-level evidence.

Built-up does not mean residential. Settlement boundaries can include roads, business land, open space and other non-residential uses.

Proximity is not causation. The study does not record ownership, spread direction, complaints or disputes.

Principal method sources: NBN Atlas, ONS Built Up Areas (December 2022) and the RICS Japanese knotweed professional standard.

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PROPERTY-SPECIFIC HELP

Concerned about Japanese knotweed near your property?

Historical records cannot answer a property-specific question. Our specialists can help with identification, surveys and a clear plan for what to do next.

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