Not sure how it is across the pond... but here it should be pre-wired. You will have to look under the black plastics under the trunk liner to find the subwoofer plug. You won't see it anywhere in the right side compartment.
Your amp would be in the left side (driver's) compartment if you have one. Here is a pic from my avin writeup that might help.
The speaker wires are the twisted pairs running along the rear and to the side over by the wheel chocks. They also go down into the battery tray because I have navigation so yours will be different in that regard. If you have no amp then your head unit may be powered and all your twisted pairs will be behind the dash I'm guessing.