Smaller scale CBRN attacks

This risk is featured in the full matrix, representing the averages of multiple different scenarios presented together.

Impact 5
risk indicator
ID 7
Risk theme Terrorism
Impact & Likelihood
Impact key
5 Catastrophic
4 Significant
3 Moderate
2 Limited
1 Minor
Likelihood key
5 >25%
4 5-25%
3 1-5%
2 0.2-1%
1 <0.2%


Malicious actors including terrorists, hostile states or criminals remain interested in chemical, biological, radiological and nuclear (CBRN) attack methods. In the UK, it is assessed that terrorists are more likely to use knives, vehicles or improvised explosive devices. However, the threat of CBRN attacks cannot be ruled out. 

Small scale hazardous events are dealt with by the emergency services on a regular basis. Some of these have a criminal element, for example in the case of illegal drugs labs. Whilst a  large-scale deliberate CBRN incident has never occurred before in the UK, two smaller-scale events challenging our national security have occurred. The first was the former Russian agent Alexander Litvinenko’s death on 23 November 2006 in London from poisoning by Polonium-210 (a highly radioactive isotope). The second, in 2018, was the attack on Sergei Skripal, a former Russian military intelligence officer, and his daughter, Yulia Skripal, in Salisbury, which was carried out using Novichok, a chemical warfare agent. This led to the subsequent death of Dawn Sturgess in Amesbury.
The government continues to reduce the vulnerability of the UK to CBRN attacks by improving methods to detect and monitor CBRN materials, including through the UK border, and by limiting access to hazardous materials and their precursors.


Chemical: The reasonable worst-case scenarios included in the assessment involve the release of a toxic chemical in an enclosed environment and in an unenclosed environment resulting in potentially large numbers of casualties and fatalities. Other scenarios include incidents which result in contamination of food or water supply, resulting in casualties and fatalities - these events could have an impact on consumer confidence and lead to adaptive purchasing behaviours. With all scenarios there is also the potential for significant economic damage.

Biological: The reasonable worst-case scenarios included in the assessment involve the dissemination of a biological agent in a smaller-scale targeted incident and in a larger-scale widespread event. There is the potential for large numbers of casualties and fatalities, and in the larger-scale event, catastrophic impacts. 

Radiological/nuclear: The reasonable worst-case scenarios included in the assessment involve the dissemination of radiological material into an unenclosed environment. The dissemination of radiological material has the potential for large numbers of casualties and fatalities in a relatively localised event. In the case of a nuclear event, the impacts would be catastrophic for the UK. There would be potentially widespread environmental damage and depending on the scale of the event, long term exclusion of areas contaminated by radioactive material. 

Key assumptions

For the purposes of the assessment, it is assumed that for certain contamination events, risk mitigation capabilities are in place to reduce the proportion of casualties that become fatalities and to limit the spread/transfer of hazardous materials.

Response capability requirements

The quickest possible response is required to save as many lives as possible. Before specialist response elements can arrive at scene the Initial Operational Response provides immediate lifesaving actions by the emergency services to minimise preventable deaths and harm for the majority of smaller scale scenarios. A specialist operational response supported by CBRN kit and equipment, is then required to manage the scene and the hazard and provide further lifesaving actions. For example, mass decontamination and specialist medical treatment might be needed. Local authorities are required to support wider consequence management. The use of the Joint Emergency Services Interoperability Principles and CBRN Joint Operating Principles ensure a coherent multi-agency response to emergencies, including those of a CBRN nature. Wider public health responses might be required under some circumstances. Decontamination of land, property and infrastructure may be required depending on the scenario. 


Recovery from CBRN incidents could be a time consuming and costly process, depending on the nature of the material dispersed. In some scenarios there could be a long term environmental hazard that may be difficult to fully decontaminate. As well as the long term physical health impacts of these types of events, affected individuals may experience significant mental health impacts and a large-scale event would put substantial long-term pressure on health services. For some events the economy could take many years to recover due to widespread cross-sector impacts.