Recently plastered walls not straight. Is that normal?

it depends what you asked for or what your plasterer priced for . Skimming is the term used for work done in plasterboard or on old walls when walls are in fair condition but unjustified to get the painter in as it will take time and wont be as good finish.. thats why when skimming is done..adding 2-3 mm and leaving a good finish for paint . leveling walls in an old house is a tricky bussiness,,... if you ask for wall to be leveled, it may mean removing either skirtings or coving, it may affect door frame, sockets and switches,radiators....are you prepared to do this? Advice should be given to clients when it comes to kitchen and bathroom walls as thats when problem like yours occour. Not ideal, but can the kitchen fitter use his expertise to ''cheat'' on the walls? ie, add a 12 mm plywood on the top of the units? my main worry would be the area where the worktop goes as thats harder to deal with for the kitchen fitter not the vertical one

If you only paid for plastering then your builder is correct.3mm of plaster will NOT straighten anything.£1000+ seems a lot of money for what you are describing though:)

Re skimming walls is usually between 3-5mm in thickness where as leveling old walls or brickwork is a completely different task (not a problem) but more money depending on just how far out they are.