One common cause is loft insulation taken too far into the eaves so blocking/reducing air circulation.
Because the air cannot circulate properly and replenish it condenses. Ensure your eaves are clear of loft insulation as the idea of insulation is to stop warm air from rooms wasting in to the loft and not to make the loft all nice and warm.
Check your loft eaves see if the insulation has been packed into the eaves if it is then clear it.
It may also be a bad designed roof structure not allowing sufficient venting so the soffit vents would be a good idea if eaves are clear. I assume the 'tiles' are roof vent tiles ask about them at the builders merchants take a digital picture or even a tile if you can remove one, on a dry day of course. Also try a net search, type in roof tiles see the different types yours might be there so you have the name. But stay with the photos too as some look the same but are not.
hope this helps.
Bob
March 2014
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