What is this Britspeak?

Tucker

Lion Rampant
#1
"I don't mind being a mug in half measures." Errf? Can anyone decipher this expression for me? Is it a common saying? A googling provided little in the way of answers.
 

LifeinthePond

Mark ov teh Pond
#6
I'd assume it means, "I don't mind knowing the half of it." Spare me the details type comment.