London's Duplicate Image Problem: The Numbers Exposing a Crisis in Digital Planning Records

At least 14 of London's 33 boroughs have identified significant volumes of duplicate images within their public planning document portals, according to an audit circulated among local authority digital teams this spring. The problem is not cosmetic. Duplicated files slow case-processing times, inflate cloud storage costs, and — in the worst instances — cause planning officers to reference outdated or superseded site photographs when making decisions on applications.

The timing matters. Sadiq Khan's City Hall has pushed hard for planning departments to digitise their entire back-catalogues under the wider thrust of the Levelling Up and Regeneration Act 2023, which requires local planning authorities to publish data in standardised, machine-readable formats. The push accelerated after the government's Planning and Infrastructure Bill entered Parliament earlier this year, piling pressure on boroughs to have clean, searchable digital records in place before new national development management policies take effect.

What the Numbers Actually Show

The audit, compiled by the Greater London Authority's digital planning unit and shared with boroughs in April 2026, found that duplicate image files accounted for an average of 23 per cent of total document storage across the portals reviewed. For a borough like Tower Hamlets — which handles some of the highest application volumes in east London — that translated to an estimated 180,000 redundant files sitting across its planning portal. Hackney Council's digital team, working with the GLA's Planning Datahub programme based at the London Legacy Development Corporation offices near Stratford, identified roughly 94,000 duplicate images after a targeted sweep completed in March 2026.

Storage costs alone are a real-money problem. Borough IT budgets typically pay between £0.02 and £0.04 per gigabyte per month for cloud hosting. When planning portals carry hundreds of gigabytes of unnecessary duplication — high-resolution site photographs submitted multiple times by applicants, identical Heritage Impact Assessment images uploaded by different case officers — the annual overspend runs into tens of thousands of pounds per borough. Across 14 affected authorities, the GLA's internal estimate put the combined wasted spend at roughly £340,000 a year.

The root causes vary. Many duplicates originate from applicants re-uploading the same images under different file names to satisfy checklist requirements on portals like Idox Public Access, which is used by Lambeth, Southwark, and Islington among others. Others stem from batch-import errors when paper records from pre-2000 applications were scanned and ingested into digital systems between 2018 and 2022 under the Historic England-funded Local Heritage List project.

Clearing the Backlog — and Who Pays

Remediation is neither quick nor cheap. Southwark Council began a deduplication programme in January 2026, contracting a specialist data-management firm to run automated hash-matching across its portal — a process that compares digital fingerprints of files to identify identical copies. The initial phase covered applications submitted between 2010 and 2020 and took eleven weeks. Southwark has not yet published final cost figures for that phase.

The GLA is funding a shared-service pilot that will allow up to eight boroughs to use a centrally licensed deduplication tool free of charge until March 2027, after which individual authorities will need to pick up licensing fees expected to run at around £12,000 per borough annually. Boroughs outside the pilot — including several in outer west London such as Hounslow and Ealing — are currently managing the problem manually, which planning officers have described internally as unsustainable given existing caseload pressures.

For residents tracking planning applications near them — whether on the Elephant and Castle regeneration corridor or along the Meridian Water development zone in Enfield — the practical effect is a portal that can load slowly, return duplicate search results, or display an old street-level photograph when a more recent one exists. Those watching applications in areas with live major schemes should cross-reference portal records with the relevant Design and Access Statement PDFs, which are less likely to carry image duplication errors, and check submission dates carefully before drawing conclusions about a site's current state.

The GLA's Planning Datahub team has set a target of reducing portal duplication rates below five per cent across participating boroughs by December 2026. Whether the eight-borough pilot produces a replicable model — and whether the government's Planning and Infrastructure Bill provides any ring-fenced funding to roll it out — will determine how quickly the rest of the capital catches up.