Most establishments in the UK automatically add a 'service charge' to the bill.
In many places this is mandatory.
Varies from 10% to 20%.
When its mandatory you get no option even if the service is crap
There is far less tipping here than there used to be. Most bar/restaurant employees etc. are paid regular wages - way above minimum wage - and dont rely on tips. In fact many tips/service charges go straight to the owner.
Much of this has arisen from our IRS making fixed assessments of tax for this type of employee well above what those people were really earning.

In UK casinos, tipping is illegal.