My mum and dad used to use one on my sister's bedroom when she moved out. They thought it did the trick. Not sure how much electricity they burn up though.

Why was it a surprise? Didn't you order it?

I have a dehumidifier which I use primarily in the winter and it's shocking how much moisture it pulls out. It works very well but the tank could do with being a bit bigger.

If you have single block work, no cavity wall, then the only way to sort the problem is to use a 45mm thermoboard (polystyrene backed plasterboard) on the external walls. It will sort the problem, have done hundreds of these jobs. It's rare that you will have damp actually coming in from the outside, especially on the 1st floor.
If it is single block work it wouldn't pass building regs today and wouldn't be able to be built , unless it's finished with thermoboard.
Basically the property doesn't have the required thermo values and with it being north facing it will cop all the bad weather.
If anyone says to use a 25mm board, they are a c**t, it will be because it's cheaper.
The only problem with this is that assuming the radiator is onthe external wall, the pipework will have to be adapted as the wall will be about 55mm further forward than the original, once it's been dot and dabbed and skimmed. Also the skirting and any coving, dado/picture rails will need to be renewed.
De hums are ok to dry out a wall before it is treated, but if you are staying long term , thermoboard and possibly a vent , with a cover that can be opened and closed will sort it properly.

Dehumidifiers work. Unless it's an industrial one, it won't use too much 'leccy. We use one all winter, and half the summer. The house gets very little sun, as it is EOT, east of the row and faces north. There is also a hill beside the house which blocks the sun until about 10am in June. However, the garden faces west, and I've probably seen more fantastic sunsets than many of you. So I suffer the damp.

Keep your windows open.

Systematically dragged down by the lawmakers