We paid the rent the whole time and wrote letters to the landlord so it was written proof but at the end of the day we were the worse off, there was no support for us. I think about the health risks, as the whole house/flat was covered in mould we had no option we slept surrounded.
We have moved 2twice since and still have infested belongings once you get them you cannot get rid of them the insects can thive on evn the smallest amounts of damp now.
I would do as paul recommends, also do take photo's I did, and write always instead of phoning so you have evidence., alway keep paying the rent, but do stress to the landlord that for safety/health reasons the property is unlivable I you may have to move out until the work is undertaked, monies which will be claimed back from the landlord for not providing suitable living conditions. Tell the landlord he/she has 'X' day's to repond, or you will notify enviromental health etc.
When we moved out we beleive our landlady had to rip all the plaster out and start again. So damp is a big problem, your landlord needs to know it is a big issue and it will get worse if not sorted now!