More Mould issues - opinions?

I uncovered some more mould at home today. Looking for opinions on possible source.

See pic below. The wall to the right is external, to the left is internal. Mould appears worse on the internal wall. I checked external wall outside and there are two very minor cracks. However their location doesn't exactly correspond to the position of this mould; they are closer to the socket that can be seen on the right.

Any opinions/ideas much appreciated.

Mould problems are usually caused by the following:

1) Lack of adequate insulation in external walls or roof space,
2) Absence of wall/window vents,
3) Absence of air cavity in external wall constuction, ie. hollow block or stone external walls
4) Rising damp due to absence of Dpc in walls
5) Poor clothes drying practices by occupants ie. drying clothes on radiators without adequate ventilation
6) Lack of adequete heating system in dwelling,
7) Turning off radiators in some rooms to save on heating bills,

found mould prev behind Christmas tree box in my walk in wardrobe, corner of bungalow: turns out some cement gone under tiles letting rain/moisture in. Quick fix.

Thanks for the replies.

For future reference, I figured out that the first bit of the wall on the left actually backs on to my open porch, creating something of a cold corner for moisture to condense on.

I did a quick fix patch job (on the porch side) with some kingspan off-cuts I found in a skip. Enclosing the porch will probably be necessary in the medium/long term.

The mould is actually aspergillus niger,not good for health especially lungs or weaker people

Guns N Roses makes some good points, I also found that washable vinyl emulsion is like putting a plastic sheet on the wall, and stops the wall breathing. Do you have an extractor over the cooker in the kitchen?