Isn't the correct version "You lie like a cheap Changi watch"?
One I heard recently about the effort equired to hold full rudder in a Meteor on one engine: "It left you with more of a trembling leg than a dog crapping razorblades!"
"MLT failure" (Master Locking Turd failure - i.e. an attack of Malta Dog!)
"Backside going half a crown - sixpence" (In a seriously worrying predicament)
And the old chestnuts like "Rare as rocking horse $hit"......