Market for cruise ships in UK

I would probably include an age segmentation as well. Yes, cruises are more relevant to the wealthy socioeconomic segment but it's also correlated with age and families. 

Secondly the frequency is also another factor that I would say differs by segement. Cruise once a year does feel very frequent and probably only the case for the over 65 and upper-middle class segement who can afford both time and cost. 

Lastly, based on the above two points, I would be tempted to even look it by number of married adult couples (instead of general population) if you were able to get that number. Perhaps more difficult for back-of-the-envelope market sizing but that would be the more relevant segementation for the industry 

Having said this, there's never a "right" answer for market sizing and so just one ex-consultants view, although I did work extensively in the travel sector including cruises.