The situation is dumb, but citizen's arrest in general is covered by laws in some counties, UK being among them.
In specific situations, a random person on the street can arrest a criminal lawfully.
This is the UK law for citizens arrest really the most important difference between this and a police arrest is the police can arrest you with the intention of finding out IF a crime has been commited, whereas you must know a crime has been commited by the person you're arresting, otherwise it's just kidnapp
Absolutely, they can. I did it several times as a security person at Walmart. The biggest difference is that a citizen does not have immunity to being sued, and a citizen can not transport. You better be damn sure you're right, or you're getting sued into oblivion.