UK restaurants receive £1.15b a year in tips despite widespread poor service, according to research from First Direct bank.
While hotel porters net £71m and bar and casino staff enjoy gratuities totalling £191m each year, restaurants easily earn the most from tips.
Customers in London and Scotland are the most generous tippers, while waiters and waitresses in the Midlands receive the least.
However, some 43% of adults admitted to tipping even after experiencing poor service.
The most popular reasons given to explain unmerited tips were "not wanting to make a fuss" (54%), and "to avoid embarrassment" (41%).
A quarter of customers also feared looking cheap.
First Direct chief executive Richard Kimber said: "A tip is supposed to be a reward for good service. But our survey shows that even in an age of consumer choice, 19 million people still feel obliged to leave a tip when they've had a rotten experience."
Separate research from credit card company American Express found that gender also influenced tipping, with women the more generous of the sexes. It also found that men wanted their serving staff to be informed, while women thought politeness was the most important quality.
Overall people in the UK spend £2.6b a year tipping.