As a landlord I am likely to be sanctioned by the local council if I let the mould persisit, the fact that you have moaned about it is great. If the landlord can prove he did everyhting in his power tos top the mould then he might have a case. So if he fitted, trickle vents, wall vents, working extraction in abthroom and kitchen, outdoor washingline or condensor/vented to outdoor tumble dryer and there was still mould, then it might be your fault for drying stuff on the radiators with all the vents and vemntilation closed/off. But he would ahve to prove he did all the good things AND you did all the bad things.
Seek out the protection info. if you were not served this info at the beggining of he tenancy or at some point this year when the law changed (cant remeber when) then he is in breach and you can sue him for 3x deposit, regarldess of any fault/nonfault damage.