Like most insurances, they always seem to find a get out clause - Firstly I would look at what your excess charge is and weigh up whether or not its worth pursuing.
I have learnt always to put polythene in the case before putting things inside and another piece on top - if you have a soft sided case. On our first cruise with Fred Olsen it was pouring with rain as we left Barbados. Obviously the cases can get wet just going from the terminal to the plane. When I arrived home my red linen jacket had bled all over my husband's cream jacket! He was not amused. It didn't occur to me to enquire about compensation. I just assumed it was my fault for not thinking of the possible problems with a soft sided case.
Hi we where on the same cruise and like you our suitcases where soaking wet when we collected them at gatwick, i have informed p&o and am looking at my insurance to see if it is worth trying to make a complaint.you should also either email or write to p&o to complain.
With the excess on insurance its not worth the bother claiming Im afraid, I always place black bin bags at the bottom and on the top of each suitcase and make sure any dark colours are packed separately in plastic if I have any whites near them. Obviously I only do this now as I have experienced the same as yourselves in the past.