Tipping London black cab drivers is a common practice, but it is not mandatory and is entirely at your discretion. The traditional "rule" is to round up to the nearest pound or leave about 10% of the total fare for a standard journey. If the driver was particularly helpful—such as navigating around heavy traffic to get you to a train station on time or assisting with heavy luggage—a slightly larger tip is appreciated. Most modern black cabs accept contactless payments, and the card machine usually offers a prompt to add a tip (often 5%, 10%, or a custom amount). Unlike the aggressive tipping culture in the U.S., a London cabbie will not be offended if you don't tip, especially for very short trips. However, if you are paying in cash and tell them to "keep the change," it is considered a polite and standard social gesture. It is also worth noting that tipping is less common for ride-share apps like Uber in London than it is for traditional black cabs.