Originally Posted by
h15t0r1an
Legally, it is voluntary if described as discretionary. You are entitled to refuse to pay it. Most of us never would refuse, however, even if faced with extremely poor service.
I've asked for it to be removed only once. When the waitress spilt 12 drinks on my friend and his phone, didn't give him a free drink or anything, and it took one hour for our lunch to arrive.
But I'm not British, so I didn't apologise for the inconvenience of them having to change the bill.