Continuity mistake: The amount of ketchup and mustard on the prison chef's apron changes between shots.
Continuity mistake: After Paddington shaves the judge's hair he smashes himself against the shop window. The amount of hair shaved is much less than in previous and further shots.
Continuity mistake: The letter D scratched into the pop up book is in white when first written. When shown again later, it's written in black.
Continuity mistake: Paddington gives chase on 'dog back' to the thief after he has stolen the book from the antiques shop, catches up with him, but the thief drops a smoke bomb and disappears. The dog is in shot as Paddington talks to the thief, but when the smoke bomb is dropped we get an aerial shot of the whole area and there's no sign of the dog.
