A processing error at South West London Pathology has resulted in more than 1,300 patients being incorrectly referred for urgent cancer investigations, following a fault that inflated the results of bowel cancer screening tests over a nine-week period.

Of approximately 17,000 Faecal Immunochemical Tests processed during the affected window, more than 4,200 returned incorrect results. Early findings indicate the cause was human error at the processing stage, rather than a failure of laboratory equipment or software.

The 1,326 patients affected were placed on the NHS two-week wait pathway, which is reserved for cases where cancer is considered a realistic possibility. Under this pathway, patients are typically referred for lower gastrointestinal investigations including colonoscopies and CT colonography scans. Both procedures are invasive. Patients who underwent them on the basis of these results may have done so without clinical cause.

The scale of the error extends across a substantial portion of South London and Surrey. Sixteen NHS trusts, 281 GP surgeries, and a single Integrated Care Board covering both regions are within the affected footprint. The geographic spread has complicated the task of identifying and contacting all individuals involved.

At a hospital level, the consequences have been immediate. St George's University Hospitals NHS Foundation Trust and Epsom and St Helier University Hospitals NHS Trust have both reported a surge in lower gastrointestinal referrals traced to the error. Triage clinics, outpatient services, and endoscopy units have absorbed the excess demand, raising questions about the knock-on effect on waiting times for patients with separate clinical needs. Endoscopy capacity in particular operates under persistent pressure across NHS trusts; an unplanned spike in referrals at this volume is not absorbed without consequence.

A formal clinical harm review has been launched, led by senior medical staff, to assess the impact on each of the affected patients individually. The conclusion of this review is anticipated for the autumn. Once it identifies which patients underwent unnecessary invasive procedures, the relevant trusts will contact them directly under statutory duty of candour obligations. Those obligations require NHS bodies to be open with patients when things go wrong and to offer an explanation and, where appropriate, an apology.

The duty of candour framework, introduced following the Mid Staffordshire public inquiry, was designed precisely for incidents of this kind: where a failure within a clinical or administrative process has caused harm, or the potential for harm, to a patient who had no means of knowing that anything had gone wrong. For those who proceeded to colonoscopy or CT colonography on the basis of an inflated FIT result, the harm is concrete. For others who were placed on the pathway but had not yet been investigated, the harm is the anxiety generated by an urgent cancer referral that should never have been made.

South West London Pathology is a shared NHS service operating across the region. The nature of the error, attributed to a human failure during processing rather than a systemic technical fault, will raise questions for those overseeing governance and quality control at the service. Whether the review's terms of reference will extend to examining the conditions that permitted the error to continue undetected over nine weeks has not been confirmed publicly.

No figures have yet been published on how many of the 1,326 referred patients completed diagnostic investigations before the error was identified.

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