Robin Smith wrote

I suppose that it may be general consequence
of the poor design of what is a converted house rather than a purpose
built flat.

Robin, in what way you think the design of your flat is poor?

If you're hanging out clothes to dry indoors, and your washer-dryer is
evaporating all the moisture that it doesn't pump down the drain and then blows
the vapour all over the flat, what do you honestly expect? As a building
designer I can (at grossly uneconomic cost) insulate every surface so that
condensation is less likely to form, but without ventilation the vapour will
then just build up and up in the air until it reaches saturation point like a
steam bath, and then you'll have *everything* going damp and mouldy. The vapour
has to be able to escape out of the building.

Yes, the builder should have ideally put in an extractor fan, and if it's
controlled by a humidistat so much the better. But I don't think this will
solve it completely. You have to play your part as well by airing the flat as
often as possible - it's vital you open a window when you have a shower, or when
you're using the tumble drier or drying clothes, so that the vapour can escape
and ultimately return to the sea from whence it came )

All the best
Peter