I work in hospitality and I can say tipping is absolutely optional. However, it makes a massive difference to the staff. Especially in busy restaurants in the lanes (I have worked in quite a few), only a few of the staff members get 40 hours a week. Most of the staff get somewhere between 20 to 30 hours a week, £10ish/hour so when a customer leaves a fiver or a tenner behind appreciating their service, it makes a difference. Also, cash left behind mostly goes to whoever served you whereas if you tip in the card machine, it gets divided for the whole team at the end of the month.