Behind the concern of the German officials is a creeping realisation that the two-year window for negotiating a Brexit, as set out in Article 50, is far too short.
An extension of the period is possible, but it would require the unanimous agreement of the remaining 27 EU member states, and is therefore seen as unlikely, or at best unsure.
Berlin is also sceptical about the possibility of Britain revoking Article 50 once it has been triggered.
This means that something will have to give, German officials say. They spell out two possible scenarios.
Under the first, the EU would revise its position and agree to a prolonged period of negotiations before Article 50 is invoked. That would win both sides extra time before the clock starts ticking, but it would represent a climbdown and probably provoke outrage in some EU capitals, notably Paris.
The second option, in the event May triggers Article 50 early next year, would be for Britain to settle for a very basic framework for its future ties with the EU, based on an existing model similar to that of Norway or Switzerland.
Even then, the deadline of two years is widely viewed as a stretch.
