At Restaurants: Service is often included; if not, tip 10–15 percent. Sometimes you'll see an "optional" charge added to the bill; make sure you're not just blindly paying it but adjusting to the level you feel comfortable with. And feel free to round to the nearest pound—up or down. Tipping in pubs is not customary.
At Hotels: Porters, 1–2 pounds per bag; housekeepers, 1–2 pounds. Go up to 5 pounds apiece at the five-star hotels.
Guides and Drivers: Tip the cab driver whatever small change you have; tipping optional for a narrated boat tour through the Thames—they'll certainly ask. Give 20 pounds per day for a guide and 10 pounds for the driver at the end of the day, or maybe take him to lunch. Not much more is expected, as Brits don't always expect to tip when they're abroad.
Dollars Accepted? Pounds much preferred.
P.S. Tipping is said to have originated in 16th-century England, and though it has since spread across the globe, England has by and large gone the way of most of Europe: Tips are included in many bills, especially in formal settings, and discretion is key in handing them over.
