Visible crew/equipment: "Resisting the aggressor down the ages" (Christmas night with the stars special episode) Just after Jones bangs the gong at the wrong time and says "that was a mistake, I'm sorry" there is a boom mike shadow on Mainwaring's union jack waistcoat.
The Armoured Might of Lance Corporal Jones - S3-E1
Visible crew/equipment: As Hodges is gathering a crowd together to witness the demonstration of how the van can be used as an ambulance, a boom mike can be seen briefly at the top of the screen.
Visible crew/equipment: When Pike returns to the arcade to tell the platoon that he has lost the boat you can see the shadow of the boom mike in Walkers face.
Visible crew/equipment: Towards the end of the episode where Godfrey goes back into the smoke filled hut to rescue Captain Mainwaring, the shadow of the camera is visible on the hut.
Battle of the Giants! - S4-E14
Visible crew/equipment: When Hodges tells Mainwaring to pull over when he is driving Jones' van you can see crew members reflected in the left hand side of the van's windscreen.
Visible crew/equipment: Bank scene: As Pike is handing the mail to Mr Mainwaring, a boom microphone is visible at the top of the screen for a second, and is quickly removed from view. (00:09:10)
The Love of Three Oranges - S8-E8
Visible crew/equipment: At the end of the scene where Pike is setting up the stall selling the lampshades, a shadow of the boom mike can be seen on his forehead just before the scene changes to the auction.
Answer: The show is a comedy, this was played for comedic effect and to show that in times of extreme fear, in this case about to be crushed by a steam train, the men had an adrenaline surge strong enough to pedal fast enough.