HC Deb 10 December 1934 vol 296 c24
54. Sir W. DAVISON

asked the Secretary of State for the Home Department whether policemen in plain clothes are being authorised to stop drivers of motor vehicles on the public highway?

The UNDER-SECRETARY of STATE for the HOME DEPARTMENT (Captain Crookshank)

There has been no recent change in the law or practice in this matter. Police on traffic duty who may have to stop vehicles are in unform, and it is only in exceptional cases that police doing other duty in plain clothes may call upon a vehicle to stop.