brussels eu u.s. negotiators say friday still need overcome large differences transatlantic free trade deal seal year factor impend exit european union britain one unite state big export market two side try agree transatlantic trade investment partnership ttip supporters say could boost economy 100 billion time growth china emerge market slow chief eu negotiator ignacio garcia bercero u.s. counterpart dan mullaney tell news conference 14th round talk side commit seal deal u.s. president barack obama leave office turn year partner make progress tariff elimination regulatory cooperation however stick eu demand include great access public sector tender garcia bercero describe u.s. offer serious cause concern likewise washington unhappy eu offer service give importance sector economies ... progress noticeably painfully slow say mullaney also say economic rationale ttip remain strong britain exit european union would force rethink large market anywhere u.s. service take 25 percent u.s. export eu imagine unite state say instance well maybe ttip apply california certain reflection party need kind developments two side previously plan produce single consolidate ttip text end july garcia bercero say likely come end september meet u.s. trade chief michael froman eu commissioner cecilia malmstrom garcia bercero acknowledge political environment become challenge environmental group greenpeace echo view many anti-ttip campaigners friday say time hit stop button eu negotiator say ttip instead positive response concern globalization want shoot shape globalization need like-minded partner share largely view say mullaney talk unique window opportunity complete ttip year allow slip away year one political transition another next years could quite pick negotiations again eu u.s. seek trade deal year know large hurdle remain