The front coil spring on my 190D broke this morning

The lowest coil just snapped while going over a small dip in the road... I inspected the front suspension just 2 weeks ago and there was no sign of any problem.
The spring is still almost in its original position (see photos) - the bottom has shifted towards the engine by an inch or two. Fortunately, the car was still drivable after the spring snapped (although I don't intend to drive it now that I know what the problem is).
Do these springs need to be replaced in pairs (left/right) or can just the broken one be replaced?
I am hoping that a spring compressor can still be inserted up the center of the spring - the fact that it has shifted may cause problems getting the compressor in. Does anyone have any advice on how to tackle this job? I am afraid of the broken spring...