James, I've had a similar problem, though not juddering. It's happened twice now in my first three days of ownership.
For example:
If I turn into a sidestreet, 2nd gear as I enter the street I am not accelerating, foot is off the gas.
When I put my foot back on the acclerator, nothing happens and I think the car is struggling. However, if I lift off the pedal and then reapply, the engine is fine.
I think my problem is the accelerator (drive by wire) not registering my pedal the first time.
Bit scary really when you consider the potential for danger that could put me in.
I'll get it looked at when they fix the ABS failure light (persistent) on Wednesday.