Terrorism laws contain extra hurdles to secure a conviction, so prosecutors and police may prefer to charge offenders with murder or assault in some cases.
Al-Qaeda and Islamic State have both encouraged would-be terrorists to use cars and trucks as weapons.
A charity is recommending the public be advised to help each other in emergency situations.
A way in for government would also allow hackers access.
For all their defiant talk of 'business as usual', savvy leaders know that any good response to a crisis is also an emotional performance.
Motivation is what separates an act of violence from an act of terrorism, and we don't know what drove Khalid Masood to kill.
Hyperbolic approaches to threat measurement don’t lead to very effective counter-terrorism policy.
Even when a response goes to plan, lessons can be learnt.
Whatever you think of her politics, May's decision to rise above divisive tough talk was an admirable one.
In the rush to compete, news organisations can still make basic errors. They need to remember the lessons of the past.
In recent years, anti-terrorism defences have become more subtle. That might be about to change.
There had been warnings and the city was on high alert. Police are now conducting a major terrorist investigation.