wet inside the wall

As you may see from the attached imaged we have come across in our sitting room a wet wall, which is located behind our sofa. I have also attached an image showing the outside area of our home, which maybe the problem to our wall being wet? Please can someone help and let me know your thoughts?

hi We have recently found water dripping into our lounge from the join at the ceiling at the bay window, we first thought it may have been a leak in the radiator directly upstairs, having taken the floorboards up upstairs the pipes are fine. We then discovered that below the bay window upstairs...