I'm a Pakistani passport holder and I'm traveling to Rome, Italy. From there, I will be taking a cruise to Malaga (Spain), Gibraltar (United Kingdom), Cartagena (Spain), Ibiza (Spain) and back to Rome (Italy). I have a multiple-entry visa for the United Kingdom and I have a single entry Schengen visa. Will I need a multiple-entry Schengen visa or is a single good enough?
You will be leaving the Schengen zone by visiting Gibraltar. If you want to to be able to continue your cruise and visit Spain afterwards, you would need multiple entrances or another single entrance Schengen visa.
You will most likely be refused check in without valid visas.