London is not actually a cruise port, but is served by the ports of Southhampton, Harwich, and Dover. Together, Southhampton, Harwich, and Dover is the fourteenth most popular port in the world, departure point of more than one hundred and ninety-five sailings per year from Cunard, MSC, Princess and more to Europe, the Mediterranean, and the East Coast.
On average cruises from London are rather expensive compared to other ports. Look at the chart below for the average cost per day by month (Cruises only depart from London between January and December). Sailings leaving from London during the peak seasons of winter, spring, and summer are a bit more expensive than the low seasons of spring, summer, and fall.