Under Fire Dad's Army: The Lost Episodes : Season 1 Episode 3

Whilst on fire-watching duty the platoon see a man shining a torch. He speaks with a European accent and has a dog called Fritz and they arrest him as an enemy agent. However, the man - Sigmund Murphy - tells them that he is a British subject and even helps them put out a fire in the church hall, after which Hodges explains that Sigmund is indeed a British citizen and the husband of his Auntie Ethel.