this adding service charge is an american thing, anyone who visits frankie and bennys ,(american owned retaurant chain) will tell you they have been doing it for years,in america apparently people are looked down on for not tipping and the expectation seems to be in the region of 15/20%
only one i've seen is at matlock bath, been going for years, gone downhill since taken over by the council.(original company went bankrupt,)even so worth seeing, this should be good