Obvious stunt double for Clifford Evans (Tom Harmon) in fight with Robert Beatty (Bob Beacham).
The murderer is able to successfully strangle his victims in a couple of seconds: the evidence suggests that in reality it takes longer than that.
The "Daily Record" detailing Sir Geoffrey Sykes' garrotting has a masthead date which appears to be Monday 28 November; however the copy of the "Evening Echo" carrying Mary's story later on the same day clearly shows the date to be Friday 19th August 1949. Additionally, both newspapers share identical columns (eg "R.A.F. 'At Home'" and "More pay for Miners").
Towards the end of the film, Robert Beatty's character rings the BBC reception desk. Clifford Evans's character picks up the phone but starts speaking before he holds the receiver to his ears and mouth. It would be extremely difficult for either end to hear if the receivers are not used properly.