Condensation or leak ?

sorry to say but if you have installed foam in your roof space the only real thing you can do is replace the roof . get rid of the foam as it stops your roof timbers breathing and rots them, the fact you are getting damp shows this system is not working and causing unseen damage to your timbers. unfortunally the foam sticks to the underside of the tiles and makes it impossible to re-use them or re-seal any that are damaged. because snow melts from the underside then slowly runs down the roof the water stays on the roof longer than rain water their must be cracks in your tiles which are alowing water ingress you can try calling this company out to rectify their fault but I wouldnt hold my breath. good luck alex

If your roof is only 16 years old it should not have needed sprayed foam on the inside as there should be a breather membrane under the roof tiles/slates if you have installed foam then the only quick fix is to ventilate with tile vents.and beware of the weetabix boards on your loft floor.