I have really bad mould in my bedroom on the exterior wall and don't know what causing it, we have our tumble dryer in the bedrooom but not against the wall and the hose straight out the window also there was mould there before we moved in. We also have it in the bathroom and whenever we get rid of it it's back within two day even with window open extractor fan on and have had air bricks installed in both rooms. Its got so bad my partner has had a reaction to it and can't sleep in that side of the flat and has to sleep in the front room. Any ideas what could be causing it?

Pictures attached are of the bedroom

You must do several things to fix this issue. Either condensation or a leak are providing the moisture, fix this. Use a mildewcide to kill the mold not just bleach. Bleach is too viscous and will not soak deep enough to kill the mold roots. My guess is that there is little or no insulation on this part of the wall allowing condensation. Add insulation and lower the room humidity with a fan or dehumidifier