Tipping in the US works well because it makes the staff helpful, friendly and attentitive as otherwise they don't make a living as their pay is so low.
In the UK if you ask to change something on the menu (I don't personally as imo it is just being picky) they often roll their eyes at you and you know they are thinking '**** off'.
I will often say keep the change. On the rare occasion that I do tip I give it to the person that I want to tip, not in the jar on the counter so everyone gets it (so half the staff are good and half are rubbish yet they split the tips equally).