trickle vents on upvc windows?

hello i had upvc double glazed windows fitted only last year and we are suffering with severe condensation on the glass and window frames.What i want to know is would trickle vents help cure the the condensation problem? if so how easy are they to fit now the windows are fitted? ive asked the fitter who fitted the windows why he didnt fit vents in the new windows when replaced my old windows and he said the old wooden windows did not have the the trickle vents so the new ones didnt need the vents!! and now hes refusing to do anything else for me!! advice would be good thank you.oh and i do have a fensa ticket!!
would cutting out the the trickle vents now make my window guarantie void?