I always delete an 'added' service charge, and if i wish to tip, I do so.
I will complain if food or service is bad - theBritish are so bad at this - they moan to each other, or other diners, and then boycott the restaurant, instead of telling the people who can put things right.
Tipping the in U.S. is far more common - indeed a lot of waiting and bar staff are taxed on their tips, the assumption being that they receive them as a matter of course, which in their cutlure is expected.
The Brits. feel it is demeaning to tip, or they feel uncomfortable, or they are just too mean.
My daughter worked as an evening waitress and found as a general rule that nice people tipped, miserable or troublesome ones didn't, even though the service given was conststant. I always approved of the fact that all tips were pooled and divided up at the end of the night between everyone - even the dishwasher got an equal share - the owner believing that all his staff contribute to a diner's experience, all should share in any rewards.