Having worked in a Restaurant, I know that tipping is an important part of the staff earnings. In general this is a good thing and tips should always go directly to the staff. I understand people disliking a tip which is added to the bill, usually this is because larger groups still leave two or three quid (but overall not each) as Lordy says.
If the menu states that there is a "Tip" (cover or service charge) added, then you have two options if the service was adequate or better pay it (and only that amount) or deduct it if the service was poor or worse and point out why.
If a tip is clearly "sneaked in" (say, via a credit card machine) deduct it, there is no moral or legal obligation to pay something you are not advised of in advance.
It is always worth asking the staff if they actually receive the tip money in some way, and if they don't - don't tip!
I believe a tip is not just for the service element but also the food, frankly bad food served well. or divine food flung at you = an unpleasant experience = no tip at best and at worst a complaint.
If you have good service, leave a 10% tip, if exceptional then more, and comment to the staff, (frankly Lordy a"couple of quid" is not usually enough nowadays - how much do you get paid for your labour?)
I take your point about tips going to the staff, I think that's important.
Not so sure about a couple of quid not being enough though, after all, restaurant staff are paid a wage, which should be at least minimum wage. I'm sure that any tips are an important part of their income, as is any part of anybody's income, but as Phil say's it's not everybody that gets a tip for just doing their job.
