@ QV, I'm not sure, but I think tipping in the UK is a token of appreciation, not a part of the income of the waiter. Not sure about that.
Here, in the Netherlands, all costs of preparing and serving are included in the price of what you eat. When enjoying the food, or the waiting, one can tip on top of that, as a bonus. It is not rude, or robbing someone from a proper income, to not tip.
Some places collect all the tips, to do something nice for all of the workers now and then. USA idea of tipping is very different from that, if I understand correctly.
@ Adam, I think the tip is best in physical money.