Not really, it's a service charge that in most places is charged for groups over a certain size (4 or 5). There is no culture of compulsory tipping for anything, because it's ridiculous.

In London I see this charge all over the place even for only two people... usually it's 10-12%.

My experience does not match what you are saying. I was always taught that (unless a service charge is already included) you should tip 10-20% in good restaurants. Not to tip I believe is generally seen as rude/a sign that service was bad.

Of course, most of us don't regularly eat in "good restaurants" - pretty much anything on the high street/your local shopping centre isn't, and anywhere you can get a meal for under £15 a head before drinks doesn't count as a "good restaurant", in my books.

I mean where you draw the line is up to you, but if there are three of you x £15, plus drinks lets say total of £64 , I would normally round it up to 70. By good restaurants I meant anything that isn't fast food (Subway, McDs). But perhaps I am not a typical customer, I don't know.

Often I go out to a restaurant with a friend and order fairly common food - totalling <£30 including drinks, and not making many demands of the staff. I don't think tipping someone to do the bare bones of their job is reasonable.

On the other hand, if I were to go with a reasonably sized group of people, had to get a table big enough for the lot of us, have people with dietary requirements or order cocktails or who otherwise make many demands of the staff... it's worth tipping as we're a pain in the ass, basically. And many restaurants automatically add a service charge in that case anyway.

Seems reasonable!

Sure, but you wouldn't leave a tip after getting a cup of tea at a wetherspoons, would you. I guess that's the UK equivalent of coffee at a diner.

Some places accept tips, and perhaps in some you should. The vast vast vast majority don't expect them as par for the course.

I have never heard of someone getting a cup of tea at spoons ;)

Ok, but I still think restaurant = tip expected. But hey, you are free to tip/not tip as you see fit.