There was one restaurant recently that didn't have one, and we almost freaked out about it.
"You can tip taxi drivers as much as you like, but most people round up to the nearest pound."
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.
Some places accept tips, and perhaps in some you should. The vast vast vast majority don't expect them as par for the course.
Ok, but I still think restaurant = tip expected. But hey, you are free to tip/not tip as you see fit.