How to tackle mildew?!!!

Hi Grummy had a feeling it might be. As a tip, next time you are looking for a flat there is a legal obligation for the landlord to have an EPC - and energy performance certificate, done so that prospective tenants can get an idea of how energy efficient the flat or house will be. If it is an A or a B then bills are likely to be very low indeed.
We have recently rented, its a fairly new building and its an A - we haven't had to put the heating on at all yet, because the fridge, computers etc kick out enough heat to keep it plenty warm enough.
If the place is warm then you don't get condensation or mildew. Of course the letting agents don't offer to show you EPCs unless you ask.
So try to find somewhere in the A - C band and don't touch anywhere with an E, F or G.
Landlords in some areas might be able to get ECO grants or Green Deal finance to improve the energy efficiency of their property if they can be bothered.

Why not speak to the local council. If it as damp as you describe it could breach standards that housing should reach to be officially habitable. The Council can make it mandatory that the landlord fixes the problem or else have the flats declared unfit for human habitation. The EPC is also mandatory and if he did not have one done and give you a copy he is in breach of the law. Again speak to your local Council.

Thanks JessM and FlicketyB, good advice, I will follow that up.

I have to say that our council here, Southend is really coming down hard on these Landlords. One recently was fined £20,000. Not that it hurt him, but at least it showed that they are doing something.

Check your lease to see what your landlord says about repairs. All the leases I've seen have outlined landlords responsibility to maintain property.