CLEAN : 4 dead including assailant in UK terror attack: police

The transcript details a terrorist incident declared by authorities, involving a car attack on Westminster Bridge and an attempted entry into Parliament. Four people, including a police officer and the attacker, have died, with at least twenty others injured. The Metropolitan Police responded with a full-scale investigation and lockdown, believing there was only one attacker. The public is assured that thorough precautions are being taken.

What actions were taken by the police in response to the attack?

What precautionary measures were taken in the area following the attack?