To not know how to get rid of the mould

Interesting! And would make the plane smell Christmasy too. I'll look it up 😊

You need something called Bactdet and Halophen to both remove the mould and destroy the roots of it.

Sometimes it can be pipes under the bath that have issues, and often one of the last places to be checked.

Any leaking pipes and any cracks in any beadwork on the roof will also cause damp

You need to find the cause. Look at the roof and gutters, look at the pointing.

Are the walls solid or cavity? If they are solid and brick it might be coming through. Do you have a chimney? Pointing, flashing and every other part of it can leak.
Is the house rendered? If there’s a crack and water gets in that will cause mould.
Is the outside soil level higher than the damp proof course? Don’t have damp proof course injected.
Is it near a bay window?
Get a new radiator that works, don’t dry clothes indoors

A chartered surveyor with expertise in damp is what you need to look for. They will inspect and give you a written report and give recommendations of work needed to fix it. They will charge you for the survey but they will not quote for the work. You will then have the knowledge of what exactly needs doing and can get quotes for the appropriate work or fix it yourselves as we did.

Don’t be fooled by contractors calling themselves damp specialists offering you a ‘free’ damp survey. They are just literally quoting you for a job that most probably doesn’t need doing. More than likely wanting to knock all the plaster off and injecting with chemicals at great expense. This solution will temporarily mask the damp for a few years but it won’t stop the cause and the damp will eventually return.

We had quotes from such companies which were eye watering.

Instead, we found a surveyor who told us the damp was caused by a leaking gutter pipe and water was pouring down the wall outside. He also told us that a damp patch on the ground floor was caused by rain water bouncing off the driveway and splashing up onto the wall. The simple solution was to remove a row of flags and replace with gravel. That stopped the splashing and the damp dried out pretty quickly after that.

It cost us about £50 to fix

Clove oil but Google exactly quantities as I was a bit gung ho with it and it turned my white paint brown BUT it worked a treat and hasn't come back.

You need a fairly decent size plug in dehumidifier

We had it on our bathroom ceiling. It was due to condensation forming in the loft and the moisture being unable to escape, causing mould to form on the timbers above our bathroom. We got some extra ventilation put in the loft and it seems to have sorted it.

We have had three dehumidifiers going round the clock for about three months now. We have got the humidity down to 40 pc. The mould has gone, the damp has gone it's much warmer now, clothes dry in next to no time and my other Half's hacking cough had gone. Even our snoring has got better. They are now set at 45pc and click in and out, after showers, cooking etc.

Do you dry your clothes on an airer or radiators indoors? If so, don't do that.

Yes you need to find the root cause. Try posting on the diy board or mse have a diy forum that's very helpful. Pics would help.

Assuming it isn't due to leaking gutter/ pipe/ some building issue, if it is lack of ventilation, get rid of black spots with a warm, dampened cloth dipped into bicarb of soda. A small plastic box of bicarb near the problem may also help or use a dish of those silica gel things that come with new shoes/ bags etc

Definitely find the root cause. We know ours is caused by guttering and roof issues but in a leasehold flat so beholden to others to get them fixed on a permanent basis. But things that have helped in the meantime...
Strippping off old damp/ mouldy wallpaper, scrubbing the wall behind with vinegar, then spraying HG mould spray leaving to dry and then spraying again.
Wallrock damp stop wallpaper, then painted with Zinsser bin primer (2 coats). And finished off with normal paint.
It's kept us mould free for 10 months while waiting for the roof to be fixed.

If you get a specialist dont get one that can offer a solution.

Don't use bleach at all. It's makes it very bad for you to breath in . Not sure if anyone else has already said but is really bad for your health .
The mix of mould and bleach together is so bad

Be careful with the sprays as they are very strong , wear old clothes etc because they will beach whatever they come into contact with .

I run a dehumidifier on every floor of our old house. They turn on and off as needed

Loads of anti mould sprays in the shops in places like Home Bargains. Plus a dehumidifier as people have said really helps dry the place out. Might be offers on dehumidifiers in Boxing Day sales

Yes, there are damp specialists, but make sure you get an independent one, not one trying to sell you services. Or, join the Damp & condensation advice Facebook group and ask on there - you'll undoubtedly get lots of contradictory advice though!

Before paying anyone I'd try all suggestions on here.
Ventilation, a mould killer and/or dehumidifier.

We have this dehumidifier and bought for a friend it's dinky but really works , never had any issues with it.
( Sorry it's a screenshot when I tried to link it kept my details!)