This topic is a bit delicate… In some restaurants (not all!) you can see a 12.5% “service charge” included in your bill normally. This is one of the reasons why sometimes eating in an average restaurant in London can be quite expensive! This is a service charge which is, in other words, the tip, but already included in your bill. This «service charge» is optional, and you have the right not to pay it. What happens is that sometimes you find it included in your account BEFORE the total sum – so it is very easy to not notice. The normal thing is that in the account you have the Subtotal and then the amount of the service charge and the Total of these two in a larger number that attracts more attention than the first Subtotal without the service charge… Then I put a couple of photos of example:
In this first photo we can see the service included in the total. At the bottom, although it does not appear in the photo, it says: “An optional 12.5% gratuity has been added to your bill thank you”
And in this second one, we can first see a subtotal of 41.55 and to this is added the 12.5% service.
As I say, although it is included in the account, it is optional. If you pay by credit card, obviously you have to ask that the service charge not be included, but if you pay in cash it is easier, since you leave what you want. Just look because if it includes the service charge, you don’t need to leave a tip, it is already included (and more!) in your bill.