He's already written the cards so maybe he'll just put them in tomorrow's papers and see what turns up. He's already had one tenner off someone without asking so maybe that's the way.
Another vote here for DON'T KNOCK.
I wouldn't tip anyone who dared to PRESUME they were getting one.
Imagine if you were out for a meal, and the waiter came over and said, "Hope you enjoyed your meal. Can I have my tip now please?"