A man drives a car into pedestrians on Westminster Bridge, keeps driving, crashes the car outside the Houses of Parliament, then tries to enter the complex armed with a knife. Four people are dead, including a policeman and the assailant, and at least 40 injured.
In the U.S. such attacks have yet to meet the $5 million damage certification threshold required to trigger the government-backed terrorism risk insurance program (the Terrorism Risk Insurance Program Reauthorization Act of 2015).
Broker Marsh reports that while recent attacks may have resulted in little direct physical damage and losses, they still have the potential for significant business disruption costs and contingency losses, for example if a city is put under curfew, or travelers cancel reservations, travel is disrupted, and business activity levels are diminished.
To address these evolving threats, insurers have adapted coverage to consider: active shooter situations; extra expense for evacuating people due to threat; contingent interruption of operations; canceled reservations; loss of attraction.
Policies can be structured to include nonphysical damage scenarios such as damage resulting from a cyber event, and nuclear, biological, chemical, and radiological (NBCR) risks.
The last major terrorist attack in the UK in July 2005 targeted the public transportation system during rush hour and left 52 people dead.
Insurance Information Institute facts and statistics on terrorism risk available here.
This chart, via the New York Times, shows that with the exception of the 9/11 and Oklahoma City attacks, there is no year since 1970 when terrorism killed more than 50 people in the United States: