Citroen Berlingo dead battery,unable to use central locking and key not working manually

I'm assuming this is the 1.9 D?
Include that next time,
Anyway the starter motor is to the front of the engine,
You'll need it jacked up for this,
find the big thick cable on the starter,
this runs directly from the battery pos+ and this is where you attach the + jump lead from whatever your using to jump it,
negative clamps on to anywhere on the engine/gearbox.
This will give the van enough V to power the system enough to open the doors.
It's a bit tight to get to the starter motor end so make this a two man job so as soon as you have a safe pos/neg connection your mate opens the door.