I can help with this first hand...
Last week I had the same problem.. recently had cavity wall insulation done and noticed higher amounts of condensation on the house... went into the loft and water was dripping from the felt.. not lots but noticeable.
I went around and checked the insulation and some muppet had actually insulated the eves and blocked the vents up which would allow fresh air in..
pulled the insulation back from the eves and unblocked the vents and also stuck 15 felt lap vents in just to be sure and within 48 hours it had cleared up.