Your V5 should tell you. Look for variant and version near top left. Version 02c is the 131PS 96kW engine. 01c is the 116 85kW engine. I say engine, it is just software that makes the difference I believe.
As far as i'm aware there is no difference between the 2 I'm sur MG/Rover only did the diesel in 2 forms the 116 & the 131 (which some refer to as 135) Same engine in the 75 or ZT. The engine is the same it's just the map in the ECU (Engine Control Unit) makes the difference.
Having a diesel myself one thing i can say is get the 160 remap it transforms the car.