Know your risk before you break ground.

There is no single piece of legislation that explicitly mandates a UXO risk assessment, but you have legal obligations under the Health and Safety at Work Act 1974 and CDM Regulations 2015 to identify and manage foreseeable risks. Many local planning authorities also require a CIRIA C681-compliant assessment as a pre-commencement condition, particularly in areas with a history of wartime activity. Failing to carry one out exposes you to enforcement action, project delay, and significant liability if an incident occurs.

CIRIA C681 is the UK construction industry's recognised standard for managing UXO risk. It sets out a four-stage process: Preliminary Risk Assessment, Detailed Risk Assessment, Risk Mitigation, and Implementation. It is referenced by the HSE, planners, and insurers as the benchmark approach. While it is not a statutory requirement in itself, following it is widely regarded as demonstrating reasonable duty of care, making it the effective professional standard for any project involving ground disturbance.

A Preliminary Risk Assessment (Stage 1) is a rapid desk study that draws on military records, bomb census data, and regional threat databases to determine whether a UXO hazard is credible and assign an initial risk rating. If the preliminary assessment identifies moderate or high risk, a Detailed Risk Assessment (Stage 2) is required: a site-specific investigation examining bombing maps, aerial photography, ordnance types, burial depths, and proposed works to produce a precise risk picture and tailored mitigation recommendations.

A Preliminary Risk Assessment is typically delivered within 24–48 hours of instruction. A Detailed Risk Assessment generally takes three to five working days depending on site complexity and archive availability. Both stages produce a formal written report containing site history, risk rating, identified ordnance types, maximum burial depths, and clear recommendations, all suitable for submission to planners, insurers, or CDM documentation.

Not necessarily. A history of bombing in the surrounding area is a significant factor, but risk is assessed against your specific site footprint, what ordnance was dropped and where, and the depth of proposed excavations. A thorough desk study may find mitigating factors (documented post-war clearance, shallow works only, or hard ground limiting penetration) that reduce the overall risk rating.

Increasingly, yes. Major contractors' insurers, development finance providers, and infrastructure clients routinely request evidence of CIRIA C681-compliant risk assessment as part of their due diligence requirements. Providing a properly scoped desk study early demonstrates a managed approach to risk and can prevent delays to financial close or contract award.

Yes. If the desk study concludes that the likelihood of UXO at your site is very low, for example, there is positive evidence of post-war clearance, the area was not targeted, or works are entirely surface-level, the report can close out the risk as ALARP without recommending any physical survey. This outcome is entirely common and demonstrates the value of carrying out the assessment early.