Not cricket

Various incarnations of the Doctor, as well as some humans, would call a thing "not cricket" when they wished to express dismay over the lack of moral correctitude of that thing. Commonly, the expression, "That wouldn't be cricket," was employed.

Soon after she joined the Fifth Doctor in the TARDIS, Peri Brown once suggested time travel could be a way to make a "killing" on "Wall Street". The Fifth Doctor immediately upbraided her, saying with an appalled face, "Really, Peri. That wouldn't be cricket." (PROSE: The Ultimate Treasure)

Likewise, the Brig told one of his men, Sergeant Houghton, that a full-frontal assault by an enemy "wouldn't be cricket". (PROSE: The Devil Goblins from Neptune)