Flight delay and cancellation compensation, Tui/Thomson ONLY

Our recent flight home from Kefalonia to Gatwick was recently delayed by sea fog. The fog lasted maybe 3 hours or so but our flight was due to land during that window. We were due to depart at 13:00. After very little info or any sort of comfort, the flight arrived around 20:00. We boarded and sat on the plane for approx an hour, then the pilot explained that he had run out of hours and so needed to take rest before he was able to fly. After this several options were floated and we chose to return back to Manchester on a later flight and then be transferred to Gatwick by coach (a 4 hour roatrip) finally arriving at Gatwick at approx 06:00 the next day, roughly 15 hours after we were scheduled.
We tried to claim through TUI, but they have advised that it was exceptional circumstances because of the sea fog. Our argument is that although some delay could be associated with the fog, the fact that they allowed the pilot to run out of flying time caused a greater delay. They did not foresee this and fly in any stanby crew as other airlines had done (easy jet for example did this).
Are they just fobbing us off or are they correct?
Anyone have any experience with this?