My family and I eat in Chinese restaurants in London often and find that we are constantly requested for gratuity on top of the included service charge when paying by card. Some restaurants even hide the fact they have included service charge, and ask for gratuity when they present you with the card-terminal.
It really seems to be across the board and we never encounter this at anything other than Chinese restaurants. It is very underhand and you could easily end up paying the 12.5% plus 10% tip.
Is this even legal?