It was Jacko Jackson (Keith Marsh) in the 70's sitcom "Love Thy Neighbour". I'm pretty sure the joke was that he'd always say he didn't want a drink in the pub, but when someone was buying would say, "I'll have half."
daisy steiner in Spaced series 1. At the house warming party the paper boy is taking "a tablet" Daisy: "go on i'll have half" Paperboy: " it's a tic tac".
jim