On Apr 20, 8:03 am, Mudchute wrote:
Yesterday morning on LBC radio Ken Livingstone said he took this
decision based on advice by the police that there had been an increase
in the number of people trying to overtake in the tunnel when the
contra-flow was in operation

So they take the security camera footage, identify the car doing it,
then get the police to stop the car on exit and arrest the driver for
dangerous driving.