Rubbish, I’m not even from a well off background or from that London but it’s been a thing my entire life that it’s normal to leave a ~10% tip for good (not even exceptional) wait service.

I will clarify that I’m talking about full service, not the McDonald’s counter, or even placing (and paying for) your food at the bar and them bringing it to you.

I knew one couple who never tipped, and they get get grief from their own kids for being cheap.