Neil Gibson suggests: If it's locked there is a way in once the door card is off. As a precaution disconnect the car battery first.
Open the wiring loom around where the window motor is situated. Look for 3 wires, blue white and yellow. There are similar wires for the window motor. Don't confuse them. Most manufacturers use trace colours but peugeot use numbers which are difficult to see.
With a separate 12volt battery you need to earth the blue wire and power up (just a pulse) the yellow and then the white wire (can't remember which one first). One is for the deadlock the other the normal lock. Open the door using the OUTER handle.
There are two solid state relays in the BSI module. They reverse the polarity to the lock actuators. If they fail (and they do) they will send a "lock " signal to the actuators regardless of whether you press lock or unlock.
If your problem is just one door the relays are ok. If you can only unlock the drivers door with the key blade but not the remote then the only way in to the passenger door is by hot wiring the lock.