The town where this episode was shot was also used in The Dirty Dozen, where it is the scene of some of the war games. The establishing shot is almost identical to the one at the opening of this episode.
The same village is used in Inspector Morse Absolute Conviction (1992)
The ducking scenes were done by Cyd Child. She could keep her breath quite long, but director Bob Asher couldn't stand watching it and had her brought up even before she gave the sign to.
The helicopter (G-AVEE) is a SUD Aviation SE-3130 Alouette II serial number 1203 (distinguished from its successor the Alouette III by its open tail boom design). This helicopter was crashed and damaged beyond repair on 7/7/1973. This same helicopter was seen in "The Prisoner".
The names Mrs Peel makes up for her children in a coded conversation over the telephone with Steed (Julian, Albert, Gordon and baby Brian) are the names of the Producers.
Reused prop: the iron maiden in the Little Storping-in-the-Swuff museum was first seen in Castle De'ath (1965).