Smelly Mouldy loft with condensation dripping from felt?

We moved into a detached property which is about 30 years old nearly 3 years ago. The moment we moved in and started putting stuff up into the loft it stank a horrible musky smell. I recently got the Christmas decorations out from the loft (before the snow) and it was its usual musky smell with slight wetness on the loft ladders. Went to put the decorations back in the loft water was dripping everywhere from the felt. Having looked a bit closely and what I initally thought was ice on the felt was infact a white mould. I can advise we have 2 brick air vents, either side of the house, it has the normal amount of insulation with a few old pieces of wood so we can rest items on for storage. The insulation does not go right up to the eves, there is ventilation in the facias, there are no down lights or extractor fans. A roofer has been to have a look and says the felt is ok and is fitted correctly. I've checked the pipes from the airing cupboard to the loft are sealed and they are ok. The reserve hot water tank for the heating I've checked and thats not hot. The only thing I can see is a very slight gap in the loft hatch which I can't believe is the cause of such condensation. Oh and we dry our clothes indoors but not on the radiators and use a dehumidifier. For it to be that smelly I'd imagine this is happening every year, but this is the first time we've ever witnessed it. I know we're not alone but what else could the problem be and how can we stop it happening again? Hope someone can help.