When the Saint leaves Penny Parker, he gets into his open top car without a hat, but in the next shot he drives through the house gates wearing a hat.
When the Saint surreptitiously enters the Lang estate he is carrying a flashlight. While rifling through the safe, it is obvious that the light beam doesn't match the movement of the flashlight in his hand.
When in Inspector Teal's office, Gordon McLeod as the inspector is talking to Detective Wilkins, his assistant, played by Ben Williams and mistakenly addresses him as Williams, his real name, not Wilkins. Williams registers a surprised look. but evidently no one yelled "cut," and the scene was obviously not reshot on this B-picture quickie.
Having rescued Count Duni from his pursuer, the Saint tangles with the man on the road. However, it is obvious from the sound of their footfalls that this scene was filmed on the studio floor and not a solid roadway.
Following his break-in at Bruno Lang's house, the Saint escapes with Penny Parker. He says to her 'I'd have had a ten mile walk to the nearest railroad station'. Bearing in mind that the Saint is English and the plot is set in London, he should have said 'railway station'.