The threat of terrorism has been assessed by MI5 as severe (see Mi5 link)  The threat was emphasised as being from CBR chemical biological radiological agents and could include nuclear devices. The effects of CBR contamination unlike explosive events, may last days to months and even years in the mind of employees who may not understand their   personal safety issues. Training and preparedness is now a major responsibility and legal duty for business and their supply chain partners if disruption, absenteeism and building closure is to be avoided.While CBRNe events are low risk high hazard, other disruptive events may be to the contrary and wide area flooding, power outage, weather extremes, pandemic and hoax calls are most likely and therefore planning for disruptive event makes real sense. The failure of supply chain companies and indeed banking and finances must now be added to the risk of vulnerabilities as the threat has emerged. 

Avian Bird Flu pandemic has jumped up the list of potential threats as new strains have developed which are unaffected by ani viral drugs currently under development. The USA has published a 200 page document which outlines their response to pandemic. It includes details of border control, quarentine and goes into great detail regarding economic slow down and public disruption.Copies of this can be downloaded (Link)