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The question is far too general. There are certain airports which are used for direct flights to embarkation ports and some that will have flights to major airports from which to fly. The best thing you can do is to sit with an agent and work out what options you have. .... Nei.
Can you fly from a local airport from Where to Where? What do you call local? Manchester, East Midlands? Which port is your cruise leaving from, Barcelona, Palma, Miami, Barbados, Southampton? If you cruise with someone like Thomson, they will quite often lay on flights with their own airline from "local" airports such as Manchester, Birmingham, Glasgow, etc, to places such as Palma Majorca or Tenerife. Other Cruise companies usually only fly from the larger airports with the option to connect to that airport from a regional one at extra cost. Try investigating booking a "cruise only" deal, which many cruise line will do, and then arranging your own flight from the most convenient airport to you. This can often work out cheaper than "all inclusive" deals.