Gordon Ramsay one of the first celebrity chefs to bring US-style 20% service charge to London
(www.independent.co.uk)
I am just imagining the logistics of this.
If the table bought $100 of food and the bill added a 20% service charge, and the party puts down $100 and leaves, refusing to pay the rest, I think that is larceny and a crime, and they could be charged.