Passenger Door Not Unlocking

Hello,

I have had my car for over year and throughout this my passenger door has had a persistent problem. My door will not unlock via the key. I know to unlock the whole car to press the button twice, however this does not work. To unlock the door I have to lift the central locking latch up from inside the car to then open the door.

The central locking latch seems to lift but not unlock. The door has some resistance when I use the handle so i do not think anything is detached. The latch on the door is very loose and easy to move compare to the drivers side. Is it possible it is not lifting higher enough to unlock and dropping under it own weight and locking again.

I have had wet foot wells in the car since i purchased it, so could it be an electrical fault or a worn component.

Any help greatly appreciated.