People do have the right to refuse the test

Two arched portable devices have been placed on the main concourse in Liverpool Lime Street station in a British Transport Police operation.

The devices are also being trialled at Southport station.

Officers said they will be deployed to different stations across Merseyside on occasions when crime is expected to be heightened, such as match days.

Members of the public do have the right to refuse to walk through the arches.

The scheme was launched in London in February as a six-week trial.