Thanks very much for your replies. As you can probably tell I'm very inexperienced!
I will get some fine grit sandpaper & sand the walls down.
The 3 drops at the stairs are fairly high, so I don't know how to reach to the top to sand them down.
If I got some soft sheen instead of matt...
My hall, stairs & landing was painted 2 years ago with Pale Citrus soft sheen. It is a new build & the plaster marks were coming through. I purchased the pale citrus (Once) one coat matt and started painting today. As I was painting, the paint was tearing with the brush strokes and I've had...