After Plymouth: What Clients Should Be Asking Their UXO Consultancy
Post 1 of 3 — a series on how the UXO sector can improve, written for clients and commissioners.
On 29 April 2026, an SC250 — a 250kg German air-dropped bomb from the Second World War — was uncovered at a building site near Flamborough Road in Southway, Plymouth. A 400-metre cordon was put in place. More than 1,200 homes were evacuated. Royal Navy and Army EOD specialists assessed the device, concluded that one of its fuses could not be reliably cleared by X-ray, and ruled out moving it. Hundreds of tonnes of sand were brought in, protective structures were built around the nearest properties, and the bomb was rendered safe through a controlled detonation on site.
By the standards of incident response, this was a textbook outcome. No injuries. Clear command structure. Public information that, while disruptive, was timely and consistent. The professionals who made that happen deserve credit, and the residents of Southway deserve thanks for their patience.
But for those of us who commission UXO work — developers, councils, port authorities, infrastructure operators — the more uncomfortable question sits upstream of the response. The bomb was found on an active construction site. That means it was found by the people doing the digging, not by the risk process that was meant to anticipate it.
This is not necessarily a failure. Risk assessments deal in probabilities, and a residual risk is not a missed risk. Ground conditions, depth, prior site disturbance and the imperfect record of wartime bombing data all conspire to make a fully deterministic answer impossible. Plymouth, in particular, was one of the most heavily bombed cities in the UK; live finds in the wider conurbation are not rare events.
What Plymouth does prompt, however, is a sharper question for clients: when you commissioned your UXO risk assessment, did you commission a report, or did you commission assurance?
There is a meaningful difference.
A report is a document. It satisfies a planning condition, sits in the project file, and gives the design team something to point to. Assurance is an audit trail. It tells you, on the day a contractor breaks ground or an unexpected anomaly is found, why the chosen mitigation strategy is defensible — and who, by name, would defend it.
The distinction matters because the two products often look identical at procurement. A typical UXO desk study, regardless of provider, will reference the same primary sources: the National Archives bomb census records, the Luftwaffe target maps, post-raid damage assessments, and historical aerial photography. The differentiator is rarely the data. It is the rigour of the interpretation, the transparency of the assumptions, and the willingness of the consultancy to articulate residual risk in operational terms rather than legal ones.
For commissioners who want to move from report-buying to assurance-buying, a small set of procurement questions does most of the work.
First, ask for methodology transparency. A defensible UXO risk assessment is not a black box. The consultancy should be able to set out, in plain language, which data sources were consulted, which were unavailable, and how each was weighted. If the methodology cannot be explained without trade jargon, that is information about the methodology.
Second, ask who, by name, owns the conclusion. UXO risk assessments are signed off by individual ordnance specialists. Knowing who that person is, what their experience profile looks like, and whether the same person will be available to answer questions during construction, is reasonable due diligence. It is the same standard you would apply to a structural engineer.
Third, ask how residual risk is articulated. "Low risk" is not an operational instruction. A useful UXO report tells the contractor what to do if a target is encountered, who to call, what watching brief or banksman support is required, and at what depth or zone the risk profile changes. Vague risk descriptors transfer the unresolved ambiguity from the consultancy to the people on the end of the excavator.
Fourth, ask about change control. If new information becomes available during the project — a deeper excavation than planned, a magnetometer hit during piling, a discovery on a neighbouring site — what is the consultancy's process for re-assessing? A risk assessment is a living document, or it is a stale one.
None of this is exotic. Most of it is in the existing UK guidance for land-based UXO risk management, currently CIRIA C785 superceding C681, and the better consultancies will already be doing it. The point is that as a commissioner, you are entitled to see it being done, not merely to receive the output.
The Southway find will be studied within the sector for years. Every new in-situ detonation adds to the institutional understanding of what current methods can and cannot anticipate. For clients, the more immediate lesson is procedural rather than technical. The quality of your UXO risk management is set, in large part, at procurement. That is the moment to ask harder questions.
In the next post in this series, I'll look at one specific mechanism that the UXO sector under-uses compared to its peers in geotechnical and contaminated land work: independent peer review.