This was originally planned as a Carl Foreman production, and he may have done a version of the screenplay (there are characters named Weaver and Grogan in the film - a trademark of Foreman's) before hiring Bryan Forbes to write the film as a planned vehicle for Cary Grant. When Forbes presented his version, Foreman said it was not good enough to present to a star of Grant's magnitude, and the project went into abeyance for a while. When Forbes formed Allied Film Makers with Michael Relph, Basil Dearden, Richard Attenborough and Jack Hawkins, they obtained the necessary rights and made the film themselves - it was a great critical and financial success.
When Elizabeth, played by Nanette Newman, is soaking,
apparently naked, in a bubble bath and taunting her husband, the white strapless bra or swimsuit she is wearing can be seen when she moves her left arm.
In the close-up of the removal van at the traffic lights the wing mirror is horizontal, but in the next shot, lights turning to green, the mirror is vertical, while in the next shot, van turning corner, the passenger, Rupert, has disappeared.
Race reads the note accompanying his envelope in close-up holding the letter in his left hand and lifting the halved banknote with his right. The shot changes, and he is holding the letter just in his right hand.