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

London's 33 borough councils collectively hold an estimated tens of millions of digital property records, and a growing share of them are exact or near-exact duplicates. That is the picture emerging from freedom of information requests filed with multiple authorities this year, as pressure mounts on planning departments to digitise backlogs under the Labour government's Planning and Infrastructure Bill, which passed its second reading in May 2026.

The problem matters now because the government has tied digital record accuracy to its wider housing reform agenda. Inaccurate or duplicated images in planning portals slow down application processing, create legal ambiguities over property boundaries, and cost councils money to store and maintain. With NHS waiting lists and immigration dominating Westminster's attention, the quiet data crisis inside local authority servers has gone largely unnoticed — but the numbers are striking.

What the Data Actually Shows

Tower Hamlets Council, which processes more than 4,000 planning applications annually according to its published 2024-25 performance report, acknowledged in a March 2026 internal audit that its digital document management system contained duplicate image files across approximately 12 percent of active planning cases. Across a caseload that size, that translates to roughly 480 affected applications at any one time. The authority uses the Idox Uniform platform, the same system adopted by Camden, Lewisham, and Southwark, meaning the duplication risk is structural, not isolated.

In Hammersmith and Fulham, the council's digital transformation team began a deduplication exercise in January 2026 covering records held on the borough's GIS mapping system. The project, budgeted at £340,000 over 18 months, aims to cleanse roughly 1.2 million georeferenced property images stretching back to 2003. Officers told councillors at a scrutiny committee in February that early scans had flagged around 90,000 duplicate or near-duplicate files, many arising from batch uploads during the 2008-to-2012 period when boroughs first migrated paper records to digital storage.

The Greater London Authority's London Datastore, which aggregates borough-level spatial data, does not currently publish a standardised metric for image duplication rates. That gap itself is significant. Without a common reporting standard, each of the 33 boroughs is effectively measuring — or failing to measure — the problem in its own way.

The Cost of Doing Nothing

Storage is not free. Cloud hosting costs for local government in England rose by an average of 22 percent between 2023 and 2025, according to figures published by the Local Government Association in April 2026. For a borough like Hackney, which overhauled its planning portal in 2022 under the £1.1 million Hackney Digital Planning Programme, duplicated records represent dead weight on a system that taxpayers already paid to modernise.

The Ordnance Survey's National Geographic Database, maintained from its Southampton headquarters but heavily used by London boroughs for address matching, flags duplicate spatial records as a category-one data quality failure. In its 2025 annual data quality review, the OS reported that London-submitted address records had the second-highest duplicate rate of any English region, behind only the South East. The figure stood at 3.4 duplicates per 1,000 records — small in percentage terms, but across a city of 4.2 million addresses, the absolute numbers run into the hundreds of thousands.

For residents, the practical consequences show up in unexpected places. A duplicated site photograph in a planning portal can mean two contradictory images of the same Bermondsey warehouse appear in a listed building consent application, forcing officers to request resubmission and adding weeks to a decision timeline. Planning lawyers operating out of offices near the Royal Courts of Justice on the Strand have noted an uptick in pre-application queries related to document discrepancies, though no firm aggregate figures for this have been published.

The immediate next step is at City Hall. The GLA's Digital Planning team is expected to publish a proposed London-wide data quality standard for planning document management before the end of September 2026. If adopted, it would require all 33 boroughs to report duplication rates annually and set a ceiling of two percent for active case files by April 2028. Boroughs that miss that threshold risk losing access to the Mayor's Good Growth Fund, which distributed £70 million to outer London development projects in its last round. That deadline, and that money, may finally give the numbers the attention they deserve.