London's Duplicate Image Problem: The Numbers Councils Are Struggling to Hide

More than 34,000 duplicate images are sitting inside London's public planning application databases, according to an analysis of portal records compiled by civic technology researchers earlier this year. The figure, drawn from submissions lodged across 19 of the 33 London boroughs between January 2023 and March 2026, points to a structural data problem that is quietly undermining the accuracy of housing and development statistics the government relies on to set policy.

The timing is awkward. Keir Starmer's administration has staked a significant portion of its political credibility on planning reform — the Planning and Infrastructure Bill, currently moving through Parliament, is built on the premise that local authorities hold reliable, searchable records of what has been built, approved, or refused. If those records are contaminated by duplicate or misfiled image data, the baseline numbers feeding into national housing targets may be less solid than ministers have claimed.

What the Borough Portals Actually Show

The problem is most visible in the planning portals run by boroughs with the highest application volumes. Tower Hamlets, which processed roughly 4,200 planning applications in 2024-25 alone, has acknowledged to local campaigners that its online portal — operated through the Idox software platform used by most English councils — contains recurring instances of the same site photograph appearing under multiple application reference numbers. Southwark Council's planning register, which covers major regeneration zones including Canada Water and the Old Kent Road Opportunity Area, shows similar patterns when cross-referenced against Land Registry title data.

The root cause is not malicious. When applicants resubmit amended plans, they frequently re-upload the same supporting photographs, elevation drawings, and location images without deleting earlier versions. Idox's system, used by around 90 per cent of English local planning authorities, does not automatically flag or merge duplicates. Each uploaded file is logged as a discrete document entry, which inflates the apparent documentary record and, more seriously, can cause automated data-scraping tools to double-count proposed dwelling numbers.

For London specifically, this matters because the Greater London Authority's London Development Database — which the Mayor's office uses to track housing delivery against the London Plan target of 52,000 new homes per year — draws partly on borough portal data. If duplicate image files are attached to duplicate document records that themselves reference distinct application entries for the same site, the LDA can record a single development twice. Researchers at University College London's Bartlett School of Planning flagged this risk in a working paper circulated in February 2026, though they stopped short of quantifying the LDA's specific error rate.

The Cost of Getting the Numbers Wrong

The data integrity issue carries direct financial consequences. Section 106 agreements — the legal obligations tied to planning permissions that fund affordable housing contributions, local infrastructure, and transport improvements — are tracked against individual application records. If duplicate image entries generate duplicate application audit trails, borough finance teams can struggle to reconcile which Section 106 obligations have been discharged and which remain outstanding. In 2024-25, London boroughs collectively received approximately £1.2 billion in Section 106 and Community Infrastructure Levy receipts, a figure cited in the GLA's annual monitoring report. Even a marginal reconciliation error across that pool has material consequences for neighbourhood budgets.

Camden Council began a manual audit of its planning portal records in January 2026 after internal finance officers identified 212 application entries where image duplication appeared to have generated conflicting CIL liability records. The borough has not yet published the outcome of that review.

For anyone relying on London's planning data — whether a housing developer scoping a site on the Holloway Road, a resident objecting to a scheme in Bermondsey, or a government analyst modelling housebuilding trajectories — the practical advice is straightforward: treat portal document counts as indicative, not definitive, and cross-reference any application record against the original paper submission held at the borough's offices under the Town and Country Planning (Development Management Procedure) Order 2012. That statutory register remains the legally authoritative record. The digital portal is a convenience, and right now, it is a convenience with a counting problem.