First, Churchill successfully urged chief constables to assist Kell’s counter-espionage operations. Secondly, he introduced a system of Home Office Warrants (HOWs), each personally authorised by the Home Secretary, which authorised the interception of all the correspondence of suspects. Hitherto individual warrants signed by the Home Secretary had been required for every letter opened. Home Office Warrants are still used today and the Home Secretary continues to be responsible for authorising them. These new arrangements proved crucial in enabling MI5 to investigate suspects.