Emma's leather dress was so expensive (over £400), that there was only one available, worn both by You Have Just Been Murdered (1967) and stunt-woman Cyd Child. They first did the scenes with Diana, then the fighting scenes with Cyd. It turned out, that it wasn't fit to fight, it had to be mended several times between the scenes on the bridge, and after completing it was completely ruined.
Both the lead actors fell ill during filming, Patrick Macnee twice being absent. This led to him having to do back-to-back filming in the evenings. At one point, he was filming scenes for three different episodes.
Simon Oates, here cast as the hired killer Skelton, later graduated to playing John Steed himself in a stage play based on "The Avengers" which had a brief London run in 1971.
A review of this programme talks of Steed's unexplained sudden wealth at the end. However, this is just a joke. It is made clear that Steed only owns a million halfpennies (1/2d). In the money of the time, there were 480 halfpennies to the pound, so Steed's pile of money is worth £2,083, 6 shillings and 8d - not a small quantity, but less than the price of a car or a house in those days.
The only episode of the fifth season in which Emma Peel wears a leather suit.