The European cruises are the summer season, The Magic Eastbound Transatlantic is usually the end of May. For the last number of years The Magic does the Mediterranean routes in June, July then at the start of August the re-positioning to Northern Europe. End of August and September is Northern Europe, British Isles, Iceland, Norway and Russia. The Westbound Transatlantic is usually near the end of September.
The Italian ports are on the Mediterranean routes in June and July
Dover, England is the home port of the Northern Europe routes, so you will have multiple cruises for this port.
Greenock , Scotland and Liverpool , England are usually on The British Isles Route
Portland , England is usually on the Westbound Transatlantic