Call them tips or discretionary charges or service charges or whatever the government has carried out a consultation on how the present system operates. There has been concern that some companies add 10 or 12.5% to bills and then essentially keep it themselves rather than give it to the waiters and waitresses customers probably think it is going to.
Quite rightly the government is proposing that it should be very clear the payments are voluntary, they must go to the workers involved, it should be clear to both customers and workers how these payments are treated.
More information can be found here
The consultation is open now and responses can be made online, it closes on 27th June.