I'm sure that the problem stems from the ground level being higher than the floor level at the back of the house. Here is the area outside the bedroom window.
The "ground" is about 5" higher than the floor and the area in the photo is concreted and haunched (right word?) up the wall slightly to stop water collecting next to the wall.
Immediately below the window though is an air vent through the wall and this is level with the ground and has no raised lip.
What would be the best methods of reducing damp ingress? I did wonder about digging it all out to lower the ground level but the drains are the back of the house seem quite near the surface and without re-doing all the drainage system, I'm not sure that's a starter.
I guess ground level higher than floor level can't be that unusual so there must be other options. I imagine building a small raised lip along the lower edge of the air vent would be a good idea.
Any other suggestions?