Also UK born and raised and I always tip in restaurants unless (a) the service was dire or (b) a service charge is already included in the bill (it will say on the bill (and usually the menu as well up front) if this is the case).
I would not say that in my experience, and I've eaten in many places across the UK, that including a service charge automatically is the default. It's more common for large parties, and some restaurants do do it for all diners, but I would say its more usual for it not to be included and a tip left at the discretion of the diner.
As a PP said, 10% is usually the standard level if you are inclined to tip.I would agree with a PP that's about to only time that tipping is 'usual' in the UK. Well, that and cab drivers. It's by no means an absolute requirement however - the system is not the same as I understand it is in the US, where the tips are intended to make up the server's income to a living wage. Servers in the UK are not paid a lot, but restaurants (and other eating establishments!) are subject to the same minimum wage requirements as any other type of employer, so there's not the same onus on tipping.
Edited to Add - I wouldn't usually tip in a hotel unless, as a PP said, my bags were carried for me.