A prominent German lawmaker has cast doubt on British Prime Minister David Cameron's plans to fundamentally change the European Union, arguing that a two-year timetable is too short to resolve the legal issues needed for a treaty change.

Norbert Roettgen, a senior member of Chancellor Angela Merkel's party, says creativity would be needed to address Britain's problems with the EU before a UK referendum planned by the end of 2017. But treaty change is a huge political venture — and Roettgen says he doesn't "see the atmosphere for treaty change among the 27 other EU states."

He says "I can't see treaty change as a realistic option within the course of two years."

Roettgen says keeping Britain in the EU is worth fighting for and preserving EU unity is crucial.