I'm not an expert on mould, but I know it's all about humidity in your house. There's a percentage which encourages mould growth, and a percentage which guarantees it'll go wild! I think the recommendation is lower than 50%. But then it gets tricky, as we don't know what's causing the high humidity. It can be caused by damp coming in, or damp being created inside. In the former case, you need to figure out how/why it's coming in (inappropriate construction, or damage to the wall/roof, or a problem with guttering taking water to the wrong place). It can come in through walls or windows or floors or roof/ceiling. If there are localized patches of damp wall, then that's easier to diagnose.
If it's being created inside, you get lots of condensation. This might be a problem with the way it was constructed, or it might be simply a consequence of you being away a lot (and probably in winter, when it's cold). Water vapour comes from kitchens (cooking), bathrooms, some forms of heating (gas, wood), and general living (breathing, drying clothes, etc.), and you might be able to improve the ventilation so it goes outside instead of inside.
Our upper floor is fine. But we had some mould on the walls in the ground floor and basement. I measured the humidity (I bought a hygrometer on Emag), and it was definitely on the high side.
I did quite a lot of work on the downstairs as we repaired/replaced walls, and then did external insulation and render. Along with new UPVC windows. Also, I replaced all the old concrete floors (thin, no rebar, no heat/water insulation) for modern standard concrete (thicker, rebar reinforcement, water and heat insulation). The percentage humidity definitely dropped significantly, and the whole space feels a lot dryer and warmer, even without any heating installed. And the upstairs became a lot easier to heat. I have not seen any new areas of damp or mould growth since then. With ground/basement floors, a lot of water vapour can pass through the concrete if there's no water barrier (as lots of older construction won't have).
But that's a lot of work. It might be that simply living in the house full-time, and having the heat on, works wonders. Or maybe you've just got a leaky or missing downpipe so that water gets pushed at the wall.
Incidentally, while I was exploring the humidity I did buy a good dehumidifier. When I parked it in the basement, it definitely made a difference. It's not a permanent solution, or a good option if there's a lot of water coming in through the walls (say). But if you've simply got a basement/lower floor with elevated humidity, it might work just to keep it in check. Similarly, I believe that an AC unit does a bit of dehumidifying too (usually while cooling/heating, but sometimes with a separate dry function too). So I have put in the ductwork for a couple of AC units, so that, if necessary, I'll have the ability to keep these rooms drier in the future.
