Factual error: Crown Court is referred to; unfortunately they didn't come into existence until 1972, nearly 20 years later. At the time of Father Brown they were 'Assizes'.
Factual error: Albert Garrity tells Father Brown about himself and his late wife meeting "Mr and Mrs Weston" on Mayday bank holiday in 1931 and it was the wettest mayday for twenty five years. Mayday wasn't made a bank holiday until 1978.
The Sins of the Father - S4-E9
Factual error: Lady Felicia is asked to sing a song she would sing in church and chose "Morning Has Broken," most lately associated with Cat Stevens, but here's the catch: Prior to Cat Stevens' rework of the 1931 English children's hymn's lyrics (by Eleanor Farjeon) to the tune of old Scottish children's hymn sang in the old Gaelic: "Child in a manger, Infant of Mary, " based on a melody called "Bunessan" (written by Mary MacDonald), the 2 hymns' lyrics and tune weren't combined into the one hymn until 1972. (00:05:00)
The Sins of the Father - S4-E9
Factual error: A character is revealed as having been hypnotised into committing murder against their will. This is not possible. (00:05:20)
Factual error: The watch that Sid sold (a gift from Father Brown) appeared to have a twist-o-flex band, but they were not available until 1962.
Factual error: During the fete sequence at the railway station there is a green van with the registration number YRL61C. Father Brown is set in the 1950s and C registrations were issued to vehicles first registered in 1965.
Factual error: A character is referred to in German as a she-devil, which is given as "sie teufel." This is German for the two words "she" and "devil" but not for the word "she-devil", which is "Weibsteufel." Or just "Teufelin." (00:32:15 - 00:33:20)
The Great Train Robbery - S7-E1
Factual error: The newspaper shown at the end, dated 31st of August 1953, has an article in it called "Enemy Claims" about the German campaign on the Balkans in 1941. (00:42:55)
Factual error: The blue Austin A35 seen in several episodes this series is three years too early - the series is set in 1953 and the A35 started production in 1956.
Factual error: Mrs. Devine's Morris Minor is a 1962 model, this series is set in 1954.