Martin supposedly died six months earlier. Ruth says she married Martin in early June 1952, three weeks before his final flight. That would place the film's action in December 1952. However, the magazine Philip held on the plane at the start of the film was from 1954 and the telegram to John had a 1954 postmark.
When Chance is at the boat, the gangplank moves between shots.
When the PO boy delivers the telegram at the boat, the boat appears to be moored in one place for the shot of his approach and in quite a different place for the shot taken from aboard the boat: the gangplank is in a different position on the boat, and the boy cycles off in a direction that would have been impossible given the geography when he arrived.
When Miss Teckman visits Chance at his flat, as he's standing by the fireplace, the position of the cigarette box on the mantelpiece changes.
Helen ( Margaret Leighton ) takes a taxi to go to Tower Bridge. She gets into taxi LLW 717, but on the journey it twice changes to other taxis before it goes back LLW 717.
When Philip visits Harris' office, the calendar on the mantle says it is Friday the 13th. Most of the date references in the film are for 1954, it would factually have to be August 13, 1954, the only Friday the 13th in 1954. The only other date reference in the film places the action in December 1952, which also did not have a Friday the 13th.
After Chance discovers the chaos of the break-in and is about to phone the police, a prominent shadow of a crew member can be seen approaching him on the back of the desk.
The boat is said to be moored at Datchet. An old church is visible from the boat - but there is no church by the river at Datchet.