On the 22nd March 2017, Khalid Masood drove a vehicle at high speeds across Westminster Bridge, knocking down several people and killing some of them in the process. The vehicle proceeded to hit the railings outside Westminster and the driver exited, brandishing a knife and stabbing police officer Keith Palmer. Masood was shot dead by armed police seconds later, but 5 people including Keith Palmer died of their injuries. Islamic State took credit for the attack and outpourings of support have been sent to London.
It was an attack by a crazy jihadist who had a history of violence but I can't help have this feeling that there has been an over-exaggeration of the gravity of this attack. People have been on the news, bellowing in defiance of the terrorist actions. For an example, just watch Andrew Neil's denouncement of Islamic State from Newsnight a few days ago. However to me, this seems a case best explained by Josef Stalin :
"One death is a tragedy, a million is just a statistic"