I have damp or sodden insulation in a wide area what should I do?

There are two possible causes for this. One could be leaking pipework or water tank in your loft space. If you can eliminate this as the cause then it is very likely that this moisture has come from long term condensation in the loft space.   

The remedy is to provide your loft with better ventilation.

Take advice from a professional roofing contractor about how to provide this.