Factual error: A number of the cars have number plates in which the numbers precede the letters, whereas at the time the letters came first.
Factual error: Eternity Ring is set in 1946. Samantha was accused of spying because she was seen with a man outside The Old Vic. She admits seeing a play there but not the play alleged (Henry V instead of The Cherry Orchard). The Old Vic was bombed in the Blitz and was closed from 1941 to 1950.
Factual error: Foyle is disembarking from a trans-Atlantic voyage from a ship which, in long shot, is painted in Union-Castle line colours. This line served African ports, not the USA. Their ships had lavender-coloured hulls from the mid-50s.
Factual error: The American flag shown has 50 stars, not the 48 stars that were on the flag at that time.
Factual error: SS officers did not carry a unit identification tattoo on the forearm, as implied in this episode. Most (but not all) carried a small, black, blood group tattoo under the armpit.
Factual error: Sunflowers are not grown in the North of France. They're grown primarily in Provence and Poitou.
Answer: He doesn't actually wear it all the time even in summer. In some episodes in the summer he simply wears his suit with jacket.