Tipping is usually not expected in United Kingdom. However, if you are satisfied with the service provided you can show your appreciation by leaving a small ‘extra’ tip. Receipts might sometimes include a service charge. If there is a service charge there is no need to tip.
Overall expectations regarding the tipping and usual tipping rates for most common categories - restaurant staff, taxi drivers, hotel staff and tour guides.
Tipping category is available in production API version 2.