I've always had the idea for a Doctor/ Leela story whare at the climactic point of the last episode they use a transmat to beam into the arch-villain's lair. Unfortunately, the transmat is slightly malfunctioning and they arrive in each other's outfits.
The arch-villain when seeing this abomination appearing before his eyes totally freaks out and promptly spontaneously combusts thus saving the universe. The Doctor guffaws outrageously and turns to Leela and winks.
Leela says "You knew that would happen!" The Doctor says "Yes, I tampered with the reciprocators. We'll have to do this more often."
Wouldn't have been allowed on seventies TV but think of the perplexing mental images created on a Big Finish audio.